I've used Mixxx http://www.mixxx.org/ which is freeware and does a very reasonable job when exercised using my (limited) DJ abilities.

However - it deosn't play WMA files.

I'm running it on a netbook (Atom 450) and it just about works if I use the "AISO for All" drivers which bypass a lot of the windows driver system. If I run it using the standard windows drivers then audio performance suffers, you get audible clicks whenever things get stressed. Any of the dual core processors should be fine (although may the dual code Atoms might still struggle a bit).