don't run the mic directly into the soundcard... the SB's aren't really built to do recording like you're doing...
i've recorded a lot of stuff for my band so have had a good amount of time dealing w/ computers and mic'ing
i recommend one of two things. if you're really into doing a good recording, you can
a)get a mic preamp for your microphone. you can either use a cheap mixing board for a budget solution, or if you want something sounding good, get an actualy mic preamp unit. the ART TUBE MP preamp is a decent one and sells for around $80.... they also make pricier models that are really nice. (you could splurge and get the professional Avalon 737, but that's $2k). you would then run the b58 to the preamp (XLR) and then probably run output from the preamp 1/4" to soundcard...
b) get a recording soundcard w/ good preamps... Emagic and terratec make some really nice soundcards, but it'll set you back a few hundred dollars.
good luck w/ the recording...