well i am certainly no guru on the subject..as i have yet to get my copy of redhat to install on my comp, but from reading my book i can say a full install with everything in redhat 7.2 is like 2 1/2 gigs (or around that) so i am guessing 7.3 wouldnt be that far off..
good luck man.
p.s. i am envious of your newer comp..mine is just a little p2 350 mhz