I found this in a few different places around the 'net - hopefully it's helpful:

Turn Off Indexing to Speed Up XP

Windows XP keeps a record of all files on the hard disk so when you do a search on the hard drive it is faster. There is a downside to this and because the computer has to index all files, it will slow down normal file commands like open, close, etc. If you do not do a whole lot of searches on your hard drive then you may want to turn this feature off:

• Open My Computer.
• Right-click your hard drive icon and select Properties.
• At the bottom of the window you'll see "Allow indexing service to index this disk for faster searches," uncheck this and click ok.
• A new window will pop up and select Apply to all folders and subfolders.

It will take a minute or two for the changes to take affect but then you should enjoy slightly faster performance.

I have just found another site with some useful speed tweaks all displayed on one page for quick access.
It is the most useful page for tweaks I have come across.
It includes the tweak you posted about turning off indexing service.

http://www.pccallouts.co.uk/freetutorials.html

It covers 18 Windows XP Speed Tweaks.

They include:

1. Remove/Replace Windows Background image
2. Edit Boot.ini to disable GUI boot
3. Disk Cleanup
4. Disk Defragmenter
5. Visual Performance
6. Windows Explorer Performance
7. Applications Autorunning on Startup
8. Cleaning the Windows Registry
9. Remove viruses, trojans and spyware
10. Apply Windows updates
11. Disable performance counters
12. Optimize your internet connection
13. Remove windows fonts
14. Disabling indexing service
15. Turning off system restore
16. Speed up boot sequence
17. Disable unnecessary services
18. Setting manual IP addresses

Thank you for your input!!

Welcome to Daniweb

good stuff