This is valid for Windows XP Home and Pro. I have observed between 4 MB to 12 MB of RAM used for the new themes.
Reduce XP Themes Resources
|Start --> Control Panel -->||Performance and Maintenance -->||System -->|
Under Performance, click "Settings" button -->
|Visual Effects Tab.
Select "Adjust for best performance."
After that, Disable and Stop the Themes Service.
Disabling of "Themes Service"
|Start --> Control Panel -->||Performance and Maintenance -->||Administrator Tools -->|
|Services -->||Select "Themes Service" -->
|Disable and Stop the Service|
I also remove the desktop picture. Why? Usually, back in the old days, the desktop picture was a ".bmp" which is very uncompressed. Since I do not like a bit map taking up so much memory (from 1.2 to 3 MB per image) I make them go away. Small tiles or .jpg's are better if you just have to have a desktop and not a blank color.
You can also check out my Windows XP Super Tweaks Page.
"Have you tweaked your OS lately?"
Choose the look:
Windows Service Configurations!!
Includes explanations of each service and advice on which services you can safely disable.