The knock-down brawl between the heirs of Hewlett-Packard and the company's management over H-P's $25 billion merger with Compaq comes to a head on Tuesday, when shareholders vote on the proposal.

The results will not be known for several days while the votes are counted and recounted - and possibly undergo Florida-style legal challenges. Since the deal was announced last September, and cleared by Federal Telecommunications Com mission and EU regulators, the battle over H-P's 1.9 billion shares has grown more personal by the day. It has, pitted Silicon Valley's two first families against Carly Fiorina, a business celebrity often described as the most powerful female executive in America. Neither side is used to losing, and analysts of the deal say it will go to the wire.

H-P founding families hold 18 per cent of its stock. Publicly declared backers of the pro-merger management at present amount to only 8 per cent, including many funds that follow the advice of the powerful pro-merger advisory firm Institutional Shareholder Services.

The heirs of the company's founders, William Hewlett and David Packard, are upset at the personal tone H-P chief executive Fiorina has taken in painting Hewlett's son Walter as a musician and academic who flip-flops over board decisions and has never worked at the company for long enough to understand it.

'I cannot explain or justify our opposition's behaviour,' Fiorina said in a recent interview. 'Our opposition...has been misleading and irresponsible.'

Fiorina believes that the computer industry is ripe for consolidation and that H-P needs to move fast. 'The technology industry is widely viewed as not mature,' she said recently. 'But I think it is maturing.' And therefore ready for a cycle of mergers.

Walter Hewlett, a lone dissenter on H-P's board, explained in a recent letter to shareholders that although he chose not to go into the family business full-time, his father had trained him for just this kind of situation. 'I really understand H-P and the businesses it's in,' he wrote. 'And I believe that qualifies me to take the stand I have.'

The family have long disliked Fiorina's combative, lead-from-the-top style of management, which included expanding the company's fleet of jets. They believe a merger, a long-odds manoeuvre to improve H-P's chances of becoming an all-round supplier on the lines of IBM, would be a reversal of H-P's famed homegrown style, the 'H-P Way', which values trust, openness and consensus.

Critics say the acquisition would make H-P more vulnerable to the low-profit personal computer market. They argue that merger could dissipate its crown jewels - the printer and digital imaging businesses - and serve only to exacerbate HP's strategic weakness in high-end servers and services.

Last week, Hewlett said Fiorina had failed to demonstrate much understanding of the company's values and history of innovation. Echoing his father's fabled business philosophy, one of Hewlett's banner headlines in letters and advertisements reads: 'A $25 billion mistake is not the H-P Way.'

Hewlett recently told analysts and investors: 'H-P's goal of becoming an end-to-end solutions company will lead to a lack of focus and has lead many conglomerates to their downfall. H-P can't out-Dell Dell and out-IBM IBM at the same time.'

He has also accused H-P's management of failing to disclose that Fiorina and Compaq chief executive Michael D Capellas stand to gain $115 million in salary, bonuses and stock options from the proposed merger. 'If the merger goes through, it will be a triumph of spin over substance,' says Amir Farman-Farma, a relative by marriage of the Hewlett family. 'They are risking Hewlett-Packard's high-margin, high-growth printer business for Compaq's low-margin, low-growth commodity PC business.'

Fiorina has staked her career on the outcome. In pushing for the deal, she is attempting to overturn a poor track record for technology mergers. She maintains that H-P and Compaq have several complementary businesses that could be harnessed together.

Given the families' opposition, Fiorina needs the votes of a large majority of institutional investors. But she has lost credibility on Wall Street by missing profit forecasts, by embarking on a complex internal reshuffling, and by trying to acquire consulting firm PricewaterhouseCoopers for $18bn.

So Wall Street is split. ISS, which advises 500 institutional clients, has come out in favour, as have three of H-P's top institutional investors: Putnam Investment, Barclays Global Advisers and Alliance Capital. Combined they hold almost 8 per cent of H-P shares.

But Banc of America Capital Management, Wells Fargo, and the nation's largest pension fund, the California Public Employees' Retirement System, plus the Ohio Public Employee Retirement System, have all recently stated their opposition to the deal.

The split could leave the outcome in the hands of some 900,000 individual investors, who hold around 25 per cent of the company's shares.

In the PR battle to win over individual shareholders, the two sides have embarked on an unprecedented campaign of full-page newspaper advertisements, direct mailings and telephone canvassing.

Hewlett says he is spending up to $32m to defeat the deal, while H-P appears to be spending at least double that in a campaign that includes two billboards in New York's Times Square. However, H-P denies spending the $70m Hewlett estimates.

In any case, H-P spokeswoman Rebeca Robboy said, the battle was his fault: 'We could have avoided this whole contest, which we certainly didn't anticipate.' On top of that, H-P is paying $33.5m to Goldman Sachs, its financial adviser for the deal, and could face a $700m break-up charge if the merger fails.

In the suspicious post-Enron business environment, the mythology of H-P's familial style of business has helped to persuade some individual investors to oppose the deal and given them a sense that they still matter.

William Urban, an investor who manages 2,200 H-P shares, told reporters he had received more than 40 ballots, as well as many phone calls, from both sides. Urban said he believed it could be a good thing if individual investors derailed the merger.

'I want to see this merger fail, because a merger this big has not been shut down by the shareholders in a long time,' he said. 'It would be sort of inspiring.'

Should the deal fail, a shake-up of H-P's management is certain to follow. Although Hewlett says the shareholder vote is not about Fiorina, he acknowledges that it would be in H-P's interest if she departed.

But if the deal goes through Hewlett expects to remain on the board. His value, he suggests, would come if the company goes off the rails - 'as I expect they would'.