Nice for editing the thread, sorry for that.
I found a helpful specification page on your system http://www.docs.sony.com/release/specs/PCVRZ24Gspec.pdf
But the problem is that it doesn't have PCI-E slot (only AGP), so upgrading is very hard. AGP is gone from the cards' manufacturers, it is very outdated. So what you might do is go make another new system
Hope this helps