MS Pamela Meyer Lopker isn't going to quibble about a few million dollars here or there; Fortune magazine describes her as America's richest self-made woman and, even though this depends on the exact share price of her company, QAD, she admits she is fantastically wealthy.

But she wasn't always worth $425 million (£300 million). The daughter of a US Navy sailor, the young Pamela Meyer studied maths and economics at the University of California in Santa Barbara. In her final year, she concentrated on computer studies, and found work without much difficulty.

But in 1979, she left her permanent job, re-mortgaged her house and gave herself two years to design software for manufacturing companies.

"As soon as I graduated I got a job in computer science. A few years later, my boyfriend, now my husband, Karl, was running a business making sandals. He kept saying `help me find software'," she says. "We looked and looked, and it was really disappointing to see that there was nothing that he could buy off the shelf, nothing for manufacturing companies. There were lots of financial products but nothing that really covered the scope of order management, financials and manufacturing planning and execution."

Karl Lopker suggested she write a programme herself, and she did.

"By this time, I had bought my own house in California and in the 1970s houses had really appreciated. So I said I'd refinance my house, put enough money in the bank for two years, go and write this software product, sell it and make a go of it," she says.

She based her new company, QAD, around the product. The firm worked exclusively with Hewlett-Packard computers, customising the programme for manufacturing companies in and around California. Between 1979 and 1984, QAD sold around 50 systems.

In the early 1980s, she says, there was little talk of a global economy; it was difficult even to buy the same computer in the US as in Germany.

"But, by 1984, we could see a trend towards common systems, a common platform. We thought that was going to be MS-DOS or UNIX - Windows wasn't out yet - and we decided it was time to create a global product," she says.

It was a smart move. At that time, the company had sales of around £1 million a year; this year, according to analysts, QAD's sales will be around $240 million.

The company designs software for manufacturing companies in four different markets:

automotive suppliers;

food and beverage and personal products manufacturers;

industrial electronics makers;

medical equipment makers, companies that need highly-regulated manufacturing processes.

The programmes, customised for each company, control everything from inventory to planning, from sales orders to purchasing and finance.

"A lot of students ask me: `What software should I write? How do I start my own business?' I always say: `Find a need. Find a need that isn't currently being filled, decide whether that need is a general need that you can stake a business on or not, then do the best you can at satisfying that need'," she says.

She makes it sound simple, but cautions that it is not and was not for her. "A lot of the time people are looking to write a programme that they can write tonight and go out and sell for a zillion dollars tomorrow. That's probably not going to happen," she says. "I mean, in 1979, I made $30,000 as an employee. It took me until 1985 before I made $30,000 as a business owner. That's a long time, and if I had stayed as a developer, I would probably have been making $60,000, or more."

Yesterday, she visited the company's new site in Limerick, where 100 skilled software graduates will soon work on research and development projects. She says the company is very happy with its decision to open here.

"Ireland gives us extremely good quality software developers in a business-friendly environment," she says. "We like the idea of the 10 per cent tax rate and that type of thing, but we look at those as transitory - you have to have the people and the business climate." The next wave of business will be based around the Internet, she believes, with companies automating not just their internal functions, but also their contact with suppliers and customers.

The Internet will automate the purchasing and order processing parts of business. Around 15 per cent of companies' revenues are spent now on orders and purchasing functions; QAD aims to reduce that to between 3 per cent and 5 per cent, she says.