If you want to record seperate instruments onto individual tracks you will need a multiple input soundcard.
To record a full band in one go you'll get away with an 8 input soundcard. That'c 4 mics on the drum kit, bass drum, snare and 2 overheads, 1 for bass guitar, one for vocals and one for guitar...leaving you 1 spare for a 2nd guitar or a backing vocal
you could just plug everything into the mixer and record the stereo out into a normal stereo input soundcard but you'll have no way of altering the individual instrument volumes once you record
Alec.