Recording Live Music (Noob)

Hey folks, my buddies’ band is playing a couple gigs this weekend and I wanna take a stab at recording em live…I have Audacity 1.3.8 and am working with a Macbook Pro, I don’t really know what goes into this, so really any general help would be great…I played around with it a bit at my buddy’s place tonight and it didn’t sound too bad, we had it running through a mixer then into a standard mic, just recording a couple of us playing guitar, set up in a basement…I think, hopefully, there will be a PA system for both gigs, and assuming this is correct, shouldn’t I be able to plug straight into it with either a USB cable or an input jack converter? I should be able to get a direct feed from the PA mix in doing this, right?

Also, is there some sort of time limit the program for recordings? Would I be able to set tracks for each instrument? Now that I think about it, the drums may or may not be mic’d, in this case I would assume I would have no choice but to us an open air mic to capture the drums’ sounds, correct?

Thanks in advanced! The first gig is May 4th so a speedy response would be awesome, this idea hadn’t really become a possibility till just recently or else I would’ve looked into it more earlier

Audacity 1.3.8 is an old beta version. You should update to the current 2.0 version.

Audacity can record several hours without any problem provided that you have sufficient free disk space.
To record multiple instrument on separate tracks all at the same time requires special (multi-channel) hardware.

Depending on your mixing desk it may be possible to run a couple of drum mics and mix them into the recording mix without them going into the live mix. You’ll probably need to consult the mixer manual for that.