In general, try and stay away from the 'we've been going for 15 years' kind of thing and go instead for first of all, what the IT company can do for their clients. For instance, do they solve particular problems for their clients, save time, help them make money, make life easier...? Be general here... For instance I know a web company who's strapline is ' we help people make money on the internet'
After that, how do they like to portray themselves- young and funky, solid and reliable...? You'll have to quiz them to find out how they want to portray themselves to their clients. After that you can give info on each member of the company (if there are only a few in the firm) otherwise profile the main players. Bear in mind users will be looking for the real flavour of the company on the 'about us' pages, so spend time to get it right.