I do have a quad. Its my memory that runs out. With out detail texture I use 1.7 gigs of memory. With I use 3. some thing. The max my 32 bit os can use.
In the modern gaming world it's become impractical to hold on to 32-bit OSes like Windows XP simply because you despise the thought of upgrading to Windows 7. Windows 7 has its flaws, but right now it's the only modern, stable version of Windows that uses a 64-bit kernel, something that many games recommend if not require of their users.
Right now, the only reason anyone could have for sticking with Windows XP is simply that their hardware is too old to warrant an upgrade.