number one thing - get everyone to work on their levels so everyone can hear everyone else. then assuming the rooms acoustics aren't too bad, you should be able to set up a pair of mics to record the band - best bet - mouth the lead vox but not loud enough to be picked up. do a separate overdub (this assumes 4 tracks enventually) for vox and then you should end of with a pretty reasonable mix.
if the band does not sound good playing together, then the recording wil suffer. the biggest offenders are players who play too loud. in electric bands, the drums can easily get covered by all the other instruments and then you'll just sound like a band in a practice room. if everyone really concentrates on playing at the right levels, you can get nice crisp drums and a full band sound.
now if you have a mixer, you can also try to isolate the instruments a bit so you have everyone playing together but still enough individual sound so you can adjust the balance into the 2 tracks. I've put drums in another room with the door open and used 2-3 mics on the drums, and also used drums in the same room but with dividers (gobos) to isolate it somewhat as well. it will still mostly come down to performance, and vocals cut directly to the 2 tracks will be risky - if the vox suck, you have to do it all over even if the instruments are working...
best bet - get a small mixer with say 8 inputs minimum and 4 busses and a 4 track recorder. you can then record the entire band with some control besides the room and performance, and you'll have 2 spare tracks for vox and/or soloing...
