Anything greater than 2GB in Windows XP is more or less a waste. If you're using 2GB and your system is crawling, your problem lies elsewhere.
That being said,
most people with a decent CPU generally wouldn't need more than 1GB.
Other things to check:
- Check your HDD for bad sectors.
- What's running in the background? Do you have any Antivirus, Spyware, Weather, etc. or other general nuisance applications stealing precious CPU cycles?
- Is Windows recognizing your CPU and RAM properly? Go to Control Panel > System. Make sure your correct CPU speed and RAM total is listed.
Also, are ONLY your Adobe applications running slow? Or is your PC sluggish in general? Are you using the latest builds of the software, or are you using much older, outdated versions?
With enough details, we can track things down with a little more certainty.