My advice having been in your situation, is make sure you get your contract/deal with the others sorted out and on papper before you start. As someone who has set up a commercil web site which still produces a good income, of which I see nothing ("I'll pay you the big bonus when another company buys us out" - it's not likly to happen) and heard at least 5 times in the last 2 years "you do the techie work for free because this idea can't fail" (They have usually don't get off the ground), I'm now far happier and welthier taking the corprate dollar or pound in my case.
Sorry if I sound negative, I guess I'm just advising a little caution, you could end up doing all the work and getting a small share.
