Welcome to the slippery slope of home recording!
Not only will you need an adequate means of providing input and output (your soundcard) but you will have to have a really hearty processor, lots of ram, a fast harddrive and, of course some software.
If you are doing a 'personal' set up, I would recommend a sound card like the Audigy from Creative labs...
http://www.soundblaster.com/products...&product=14065
It has all you will need to plug in you and someone else and do a nice 2-track session.
If you are going for the full-blown studio, you can find products from M-Audio, like the Delta 1010
http://www.m-audio.com/products/en_u...1010-main.html
My friend has 2 of these along with a whole rack of processors, eqs, patch-bays, and so on... And believe me, he never stops buying and upgrading his stuff... He is SO addicted...
So beware - once you figure out your thing you are on your way to becoming a home-recording junkie! It is an expensive, but very rewarding habit to develop!
Good luck!