Home recording studio questions

I have a co-worker who is aiming to build himself a recording studio in his house. Ive helped aim him in some directions for amplification and monitors, he is on somewhat of a budget, but he seems to have come across some stumbling blocks.

He is currently thinking of using a computer for the main system. He is an aspiring rap artist and needs to be able to input analog signals such as vocals and live instruments and digital samples and loops, mix and coordinate it, then be able to record this to a CD.

Does anybody have any reccommendations for computer hardware that is not TOO costly (not thousands of dollars) that he could use for this? It looks like he already has his software picked out, but he needs a real good interface that will be flexable and give him the capabilities to do what he wants to do.

Any reccommendations? Anybody here built a recording studio based around a computer? If so, what are you running?

He is getting some advise from some computer guys, but they seem somewhat hung up on MP3 and stuff. I know that he is looking to be able to make real quality recordings.