So, my nerdy friends, is an external soundcard for a latpop something I can buy? I've got a good sound system I've borrowed from a housemate but only one audio plug to slot it into. Is there some sort of device that will allow me to plug in a 5.1 system (minimum)?

Soundblaster Audigy 2 ZS Notebook is a PCMCIA card that will do it. Optical link for 5.1. They have a USB version too I think. Check the Creative website.