I'll second this! If it's live, then it's a good idea for a mixer/amp. The Shure SM58 is the workhorse of the musician's trade, as it can be used to mike both instruments and voice. Be warned, you will need to get a XLR/Balanced cable for it. It uses three wires for the sound, built in a way to cancel out interference. Use these types of cables as much as possible, it will keep your sound cleaner! And don't skimp on cables!!!! The last thing you want is snap/crackle/pop from the wires in the middle of the performance.

If you don't want to do live sound, just a basic mixer is a good bet. Behringer makes some good basic mixers with XLR, 1/4" and RCA stereo inputs. Go down to Steve's Music and talk to them. The people there tend to know their stuff.

ttyl