512MB is the VRAM size. The 3rd party GPU makers liked to load cheap cards with tons of VRAM to increase sales. It's a marketing thing. They can sell old parts by fooling people with more VRAM. I have and old AGP nVidia board that I flashed into a Quicksilver Mac. It only has 256MB but it is one of the higher end boards. They came out with a 512MB model later, but as years went, the resellers needed to get rid of excess so they'd load on old parts and give them more VRAM as a selling point. AGP cards didn't really die till...oh...it was a few years after nVidia or ATI stopped making them. They used a bridge chip in them to get them to work on AGP sockets. However, most of them, were ATI boards, not nVidia.
So that could be something like a 7900 series, G71 chip. Or it could be total crap that a reseller bundled. If it is a 7800/7900 series card then that is roughly a PS3. Literally what Sony did was slap a G71 into the PS3 and called it a day. It didn't have a custom chip like the Xbox 360. Either way, that is plenty of power to run GOIO. How well it runs it, dunno. You'll find out.
