xp actually supports 3.5 gigs of ram so getting 2 more gigs of ram would be very smart. Those 2 extra gigs will provide a huge increase in performance and will make the bottleneck on the 260 smaller. I would advise that you get the extra 2 gigs over a new cpu for now as that will have a bigger difference.
Not true at all. First of all, he would need a 64-bit OS. You don't really see much of a performance increase between 2GB and 4GB in gaming. When using very memory intensive applications such as Photoshop and any editing software, the extra 2GB kicks in.