Purplemattfish said:we have either the long answer or the short answer?
well here is the short answer: Cause Windows XP 32Bit just dont ok!
and the long answer: It is to do with the compilation of the OS which results in a maximum logical memory space that the system is capable of using, the more memory you add the slower/more complex it is to access that memory in an efficient manner therefore as a compromise Micro$oft limit the OS (XP 32Bit in this case) wheras XP 64Bit has a higher limit at the expense of more complicated memory handling (I inadvertantly typed mamory there you can tell where my mind is drifting)
for more info see:
http://hardforum.com/showthread.php?t=1035670&highlight=/3gb Yawn
http://forum.beyond3d.com/showthread.php?p=1019652 snooze
http://www.brianmadden.com/content/article/The-4GB-Windows-Memory-Limit-What-does-it-really-mean- Yawn Yawn