Hardware/Software for 4 to 6 channel audio recording

I am looking for some advice on recording audio. I would like to be able to record somewhere between 4 and 6 simulaneous channels of audio. Currently I can only record 2 channels, so I assume I will need new hardware and software. I want this to be protable, so en external (USB/Firewire) or PCMCIA solution would be best.

I would appreciate any advice on this subject.