Hello there matey, I can offer some limited help for you with this having had a go myself.
Firstly your going to need an external USB soundcard, the mic socket on the laptop your planning on using really won't be upto the job. With the levels you'll be belting into the thing it will distort, badly. So an external sondcard with line-in from yor mixer is going to be your best bet.
3.5 gig should be more than ample, you'll probably find your recorded one hour mix won't be anymore than 650 meg (approx) in wav format on the laptop. I remember recording live sets off the radio via my personal stereo through to my PC and that was a lesser spec than your laptop (P2 350 256 ram and 8 Gig HDD)
Get yourself a 4 Gig USB memory stick if you haven't got one so you can get the mix off the laptop and then get it on the PC if needs be so you can compress it into mp3 should you want to upload it
Application wise, hit yourself up with audacity, it's free
As many people here will say it's a very good little app.
Out of interest what style are you mixing ??
Hopefully I've been more help than hinderance