Good luck, i'll be interested to hear if you resolve it or not. There's lots of tweaks that i know for XP to improve performence but to be honest, with the system you have, you shouldn't have to tweak. Fast processor, you're board is very good, normally stable and a good graphics card, only the Ram lets you down
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May also be worth your while to run a full scan on your hard drive, to include the surface scan. Never mentioned it before as you said you have no probs running other software. They may not be as memory intensive as photoshop though. So you may as well check it out. If XP performs like you expect it to then it certainly seems like it's hardware related. As great as XP is lots of people have problems with running applications. It sucks really that i had to pay for the full version when i should have been able to purchase just the upgrade but it's not a good choice right now. Way too many problems with upgrading.
Wish i could just pop over, be a lot easier to diagnose. I know you're searching for articles relating to photoshop but i really think it's down to your particular system. There's a piece of hardaware in there right now that's not particularly happy and the no1 suspect is ram, followed by hard drive, followed by motherboard and lastly video card, though unlikely.