One of the problems with music recording on any PC is having good input and output devices. Your computer speakers and microphones are NOT up to the job of doing good sound.

If you're getting lousy sound, it's probably trying to listen using the computer's standard speakers. If you go through the links above, you will see that most of them are designed to enhance part of the audio frequencies, and are not flat across the board. You would have to take that into account before burning a CD from what you mix.

As hesperis said above, take your microphones, plug them into a pre-amp, and THEN put that into your sound-card's Line-In port to get good sound.