What I like about the Xbox is that you can buy the version that's right for you "right now". Let's say that during the holiday season, you'll be wanting to save some cash, well you got the arcade version which you can "upgrade" later by buying the harddrive.
Then you'll have a nextgen console for a reasonable buck.
I've been wanting the new GTA to come out for the pc... Never came. My xbox suffered the RROD here a couple of months back, and the worst part is that it's a couple of months after warrenty... Gah!
The PS2 doesn't have close enough power specs to run GTA 4. Your best bet is to get a PS3 or 360 and since your on a budget get the 360 arcade with a memory card. Any new 360 has the updated cpu and gpu dies and heatsink so RROD shouldn't be a problem.