Audio using home computer

I have a dell desk top computer. I use iTunes to organize my music. Currently I listen to the music on the Harman Kardon speakers that came with the computer. I'm ready to invest in some high end equipment. Is there equipment out there that interfaces with a computer so that you can store CDs on a harddrive and download music from the internet (iTunes)? I want to use this in my office at home. Any suggestions or places to look?

Peter