80 gigs on thee hdd is a bit low, but if u have less than 3 games assuming, no video or music downloads and all mmorgs, then ur system will be fine for at least 2 yrs.
With 80 gigs it can fill up to 50% to 75% within a 1 to 2 years with lots of mmorg expansions.
I would start out with a 160 gig for about 50 dollas
u can find it at www.pricewatch.com
or here: http://www.pricewatch.com/hard_drives/eide_160gb.htm