Shaun SS,
The link cordura21 provided pretty much gives your firewire options, but for recording with a laptop, you do have another option: PCMCIA. There are audio interfaces from both Echo audio (
http://www.echoaudio.com) and RME (
http://www.rme-audio.com) that use a PCMCIA slot.
I use my laptop to record live gigs in small clubs and bars to help pay for the toys I play with at home. I use
a Layla Laptop (PCMCIA interface from Echo) with a Layla EXP to bring me up to 16 channels of input. Maybe I can offer some advice.
First off, taking the main outs from the mixer never seems to work out. The mix that sounds good in the room doesn't always sound good recorded. In particular, the vocals and keyboard are usually much too loud, the drums much too weak. I also find that many bands have too much effects put on when recording live that sounds awful on the recording. Plus most of the bands mix in mono in these situations, and a stereo recording is nice.
Setting up room mics works sometimes. It depends on sound of the room, and if you can get decent mic placement without running cords across the dance floor or putting your mics in harm's way in a room full of drunks.
I'm always happiest when I record each instrument to be mixed later, with my own effects added. How I get the input depends on the band's mixer: if it has outputs for each individual channel, I will plug those outputs into my Layla for each vocal mic, keyboard, and drum mic the band happens to use, plus maybe the bass. I always have to add overhead mics to the drums, and sometimes the band has no drum mics at all, so I have to mic the whole kit. I also mic the guitar cabinets (it just always sounds better that way), and sometimes the bass cabinet, depending on whether the band runs their bass through the main PA and what kind of sound comes through. Also, as long as I have inputs left open, I will add room mics, in case I can get the sound I want from them, or to just add in more audience noise at the end of songs (the bands like to hear recorded applause

).
If the band's mixer doesn't have individual outputs (or they don't use a mixer.

), I mic everything -- drums, bass cabinet, guitar cabinet, and I have the vocal mics plugged into my preamps. I send the vocals to the band's mixer/PA from the Layla's outputs (there's 8 of 'em).
Note that either way, 8 inputs is never enough. You can get it down to 8 by submixing drums through an auxilary output on the mixer if there's one available, but the drummer has to sit and play for you at actual volume while you set it up, and that sometimes pisses off the bar patrons.
Just some thoughts to consider.