I got the beta earlier today and love it; Windows has finally actually put together what appears to be a fairly fast, easy to use, stable, product. That said, I installed it on my second computer and am still running vista on the primary computer just to play it safe, while it appears to be a stable beta, it is still a beta, and unless you are comfortable dealing with the possible problems that could arise, and the potential for data loss, I might stick with XP for the time being. Also I did have some strange issues with the aero graphics after Windows 7 installed my graphics driver automatically, in fact it seemed to take care of a lot of that stuff through the windows update pretty well) but after messing around with the drivers a bit it seems to be working fine now.
As far as your specific computer, Windows 7 does seem to be a bit less of a resource hog then vista was, but half a gig of ram isn’t much, though I have heard of people running it on lower power systems, if you are comfortable with backing up, doing clean installs, and all that stuff I guess it can't really hurt to try.