Get a dual core system - that will relieve a lot of resources and allow you to run multiple programs (go quad core if you can afford it). Most modern pc's will have more than enough in terms of processor speed - also make sure the soundcard is for music production. Creative Labs do some good entry level cards - make sure it has a 1/4" in line connection so you can plug guitar or other instruments straight into your computer. It would also be handy to get one with a midi connection in case you want to connect a small cheap keyboard.