If you are thinking of starting on your own, partnering is probably one of the most important things that can make or break your venture.
And am pretty sure you have concerns and doubts about ownership and how do you allocate it fairly between the founders? And who exactly is a founder?
Tough question to answer. Joel Sposky has done a fabulous job of answering it in detail here. I tend to agree on most things including on that of not treating a non-full time partner as a founder.