Mal,
I've been watching this thread for a while now ... I wouldn't want to see you spend money on a new system, if it wasn't really called for.
If I put it in car terms: It sounds like you have a glitch with the fuel supply to the carby when you try to accelerate hard, and your saying you want to replace the whole car because of it?
Seems a little drastic.
Has the issue always been present on the system? If not, what changed on the system before or at the time it started? Is it only on Photoshop? Have you installed any new plugins? Did you try running photoshop while the system was in safemode?
You say your running an Intel Core Duo CPU T9500 @ 2.60GHz. Then I would assume your running a notebook, as the T9500 is a mobile processor. Is the D Drive you use for a scratch disk a seperate drive or another partition on the same drive as C: ?
Did you try the method Rick mentioned about looking at what is using your memory? (below)
Two things I would test first -
1 - Disable your plugins / move them to a temporary folder. (AFAIK photoshop has a hard limit of how much memory it allocates for plugins.) Try running PS without any plugins.
2 - Recreate the preferences file:
To re-create the Photoshop preferences files:
1. Quit Photoshop.
2. Rename the Users\[username]\AppData\Roaming\Adobe Photoshop CS3\Adobe Photoshop CS3 Settings\Adobe Photoshop CS3 Prefs.psp file to Adobe Photoshop CS3 Prefs.old.
3. Start Photoshop. Photoshop creates a new Adobe Photoshop CS3 Prefs.psp file.
Alternatively, use the Adobe troubleshoot checklist.
Troubleshoot system errors or freezes in Photoshop CS4 on Windows Vista
Do those, let us know the results, then we can guide you from there.