I'd recommend running a mic preamp between the soundcard and the mic. ART makes a couple in the 70-90 range (1 has SPDIF, which is good if your soundcard is compatible) and Behringer makes a knockoff for around 50.
If you want versatility, where you can run multiple mics/inst., you can pick up a small, 4-channel mixer, which most have built-in mic preamps. I have a 4-channel (2 mono + 2 stereo) made by Behringer that has built-in pre's that I run everything through into my computer... I think I paid $75 for it new.