Sorry, can't be president (born in England). But as far as I know there is no reason you can't start a company on a student visa. You can't be hired by someone else's company, but you don't have to be a US citizen or resident to own a company based in the US.
Oh We can definitely own a company alright! But the problem is with time/mind space. Currently my entire spring break is dedicated (to pretending) to study for my Qualifier exams! I am hoping it will be better once I finish the requirements and start on the thesis. But it has to be moonlighting I guess, the visa has us cornered.
At Viaweb, two of the three main hackers (Robert and Trevor) were in grad school the whole time and actually got their degrees. In fact, Trevor got his a day or so before the Yahoo deal closed, and was the subject of Viaweb's last press release:
http://www.paulgraham.com/tlbphd.html
I believe some cofounders can still be in grad school, as long as at least one isn't.
I dont know about UK citizens, maybe there is an agreement by UK and USA but citizens from india cannot start a company or work on anything else other than the visa they are assigned.
