Tut tut doomey. P2P is legal, but what you use it for could be ILLEGAL!
What do you want it for? Forget Limewire, it's full of sh**ty
viruses! The ones l like (all free) are:-
DC++ 0.674 (this older version is the best)
Ares 2.0.9.3030 ( DO NOT use Ares Galaxy or Ares lite ) This is the only P2P that allows you to see the file as it is downloading. You can then delete it if it's not what it says it is rather than wait for it to complete. It's a bit slow though.
BEARSHARE also gives good results, but you have to wait for the download to complete.
Whatever you use them for, make sure you have a damn good virus protector that is kept up to date.