The default setting for WindowsXP is to cache the Explorer settings for 400 folders.
To increase it:
1.Start Regedit
2.Go to HKEY_CURRENT_USER\Software\
Microsoft\Windows\ShellNoRoam
3.Change the vaule of BagMRU to whatever size you want (hex)
1000 - 3e8
2000 - 7d0
3000 - bb8
4000 - fa0
5000 - 1388
You can Dowload a reg file that will set it for 5000