There are almost no upgrades left available for this computer. You can no longer find the processor upgrades, not that there was a noticeable difference from this processor to the 3000+. This uses an AGP card. The card that is in it has VGA, DVI, composite and HD Component out. You could up that RAM, but for XP you won't notice much of a difference from 2GB to 3GB.
The power supply rating is 250 watts with 10Amps on the 12v rail.
This system is great if you want a small form factor that plays MAME great. If you want to be able to upgrade and change a lot of components, then this is not the computer for you.
Jeff