Check out some firewire interfaces. M-Audio 18-14, Digi 002/002r, Mackie Onyx 400F, Motu Traveller, Presonus Firepod. I think this would be a good place to start. You just connect them to your Digital Audio Workstation (DAW) via Firewire (IEEE 1394) connection, and you can multitrack to your computer.

Connection the Main Out's from a mixer to wouldn't do what you'd want it to do, you'd get a stereo signal sent to your DAW and it would be recorded on two tracks (LEFT and RIGHT mono). This wouldn't allow you to do any mixing after the fact, all mixing would have to be done while recording.

1. Direct out
or
2. Send
or
3. Aux send prefader

Generally, less electronic circuits in the path is better, especially inside cheap mixers.

Firepod

try looking at the Presonus Firepod 8 mic pre, firewire conection its a good start, there are many other options also, just keep reading and searchin u will figuer out what might work best for ya