Ive run a few different distributions in a dual boot configuration with xp.
Ive tried redhat, fedora core 3,4, gentoo, ubuntu, arch.
I would say if you want a no hassel easy installation then ubuntu is a good distribution to use and if you want to learn how to compile a kernel, setup everything manually to have a look at the gentoo documentation they have on their site because its very good.
I think linux is improving all the time, i would probably stick to it perminently if/when wine's directx implementation is finished and i can play all the windows games i want on it with little hassle because thats the only thing keeping me using windows really.
When vista comes out it will probably drag me back because of their dx10 implementation which will probably take ages to reverse engineer into the wine project.