It's hard to imagine a world without Windows. Although Microsoft's operating system has never inspired anything like the devotion enjoyed by its Apple counterpart, it long ago achieved something even more important: critical mass.

Kit out your office PCs with Windows and you can sleep safe in the knowledge that with few exceptions your business partners, customers and suppliers will have done the same. They're probably also using many of the same applications, which means that mailing a Word or Excel file to another office is unlikely to cause problems. Windows may be far from perfect, but the fact that everyone uses it makes life a whole lot easier.

So what are the chances of Linux raining on Windows' parade? Already established as a secure, stable operating system for servers, Linux is now being touted as a serious alternative to Windows in the desktop market. As an open source product, it's certainly cheap.

You can now buy a PC running a Linux variation (the contentiously named Lindows) from Evesham Micro for around £250 and specialist distributors such as SuSe and Red Hat are actively promoting their own desktop-friendly Linux packages at prices significantly lower than Windows. This should make Linux tempting, but only if it is also possible to acquire the additional software necessary to run a business. So what is available to Linux users?

The good news is that when it comes to office basics, Linux users are well catered for. If you buy Linux from a distributor rather than downloading a free version from the web, the chances are it will come bundled with Open Office, a suite of applications that includes word-processor, spreadsheet and presentation tools. Like Linux, it's an open source product and you can load it on to as many machines as you like without paying for additional licences. It is also available as a free download from www.openoffice.org, but support is limited to an email response service and online documentation.

Abandoning familiar applications may not be popular with staff who have grown comfortable with Word or Excel, and this has long been a barrier to the widespread adoption of Linux (or any other operating system) on the desktop. But opting for Linux does not necessarily mean that you have to throw away Windows applications. Crossover Office (download for $54.95 from Codeweavers.com) will enable you to run a wide range of Windows software, including Word, Excel, Powerpoint (the 2000 rather than XP releases), Lotus Notes and Quicken.

Jasmin Ul-haque, UK director of Linux distributor SuSe, argues that the launch of Crossover Office represents an important step forward in positioning Linux as a viable desktop product. "People are aware that Linux can reduce their software licensing costs, but they are concerned about training and migration costs," she says. "Crossover Office reduces the barriers." SuSe is currently making a concerted effort to promote Linux as an alternative to Windows and it includes Crossover Office in its own Office Desktop package, priced at £89 with 25 user licences.

Crossover Office is built on technology developed under the umbrella of Wine, an open source software project aimed at building a workable means to run Windows-compatible applications on Linux-powered machines. You can download free Wine software from www.winehq.org, but you won't get the support offered by Codeweavers, particularly in terms of telling you accurately which Windows software works and which doesn't.

If you have no great desire to hang on to your Windows applications but find Open Office a tad under-specified, you could try Sun Microsystems' Star Office, a commercially released product costing between £16 and £32 per user, depending on the size of the order. In fact, both office suites are based on the same core software (with development funded by Sun) but the paid-for version has enhancements such as a calendar, mail client and database. According to Mru Patel, head of desktop solutions at Sun, Star Office also appeals to business users who require "support, bug fixes and a roadmap for upgrades". It is, he says, cheaper than Microsoft Office, while being fully compatible in terms of sharing files. Each user can run it on up to five machines.

At the meat and potatoes end of the office software market, you generally have a choice between free open source products, which work perfectly well provided you have a certain amount of technical expertise and don't require support, and enhanced commercial counterparts that you pay for. However, if your business requirements run to multi-user groupware products, the bills begin to mount.

For instance, SuSe's Open Exchange Server offers the kind of functionality that you'd expect from Microsoft Exchange and Outlook, including email and coordinated calendaring. It's a proprietary product, costing £1,400, with the cost inclusive of 10 groupware users licences and unlimited email. Similarly, Sun Microsystems has just launched Small Office Solution, combining Star Office with a server package that permits groupware functions and remote access to the office network via PDAs, smartphones and laptops. It costs £9,000, with 50 user licences.

Once you get into the heady realms of customer relationship management, enterprise resource planning and accountancy, the server-based products that dominate the Windows environment have also been retooled to run on Linux. For instance, SAP's various MySAP applications (which include CRM, ERP, supply chain management and accounts modules) run on Linux servers, as do the components of Oracle's all-embracing E-Business suite. These companies haven't yet produced applications for Linux, but according to Oracle director of product marketing Gary Pugh, the operating system is rapidly becoming irrelevant: "Applications are moving from the operating system to java-equipped browsers. That is opening up the desktop to Linux."

The upshot is that while Linux can cut your operating system costs to virtually nothing, the chances are you'll still be paying significant sums of money for business-critical applications.

Help panel
What is Linux?

Linux is an operating system that can be used on servers and desktop computers. It is an open source application, meaning, in effect, that no one can patent the software or impose licensing restrictions on it.

If you download a free copy from the web, you can load it on to as many machines as you like.

However, most business users tend to buy so-called distributions from commercial vendors such as Red Hat or SuSe. These vendors can't charge for Linux, so you pay for added value services such as support, easy installation routines, documentation and bundled software.

These extras may be the subject of licensing restrictions, so read the small print.