SpeeDefrag and Easy Cleaner (google for) are long established and rock solid free tools which you might find very useful, John.
SpeeDefrag is far better at defragmenting your drive than the built in windows job, and you can leave it run and it'll turn off your PC when done.
easy cleaner from toni arts will clean up the registry as well as any unecessary files, duplicates, cache etc.
Cleaning up the registry is good practice anyway.
Easy cleaner is fully "undo-able"
set your windows cache (internet cache) TO 80MB, you dont need more than that, 80mb has always been the optimum for all the windows, from 98/SE/Millenium through to XP XP pro etc.
Consider turning OFF system restore which is a real hog on disk space. Of course if you do this backp of important files is of paramount importance (well, it always should be anyway lol).
Drop your recycle bin settings to, say, 2 percent of your drive space. 10 percent is default. this will free up more useable drive space.
Turn off drive indexing.
If its a work machine, are you using too much RAM for (eg) onboard graphics? Try reducing the graphics allocation for your RAM
go to start/run then type msconfig - here you will find all the startup programs which start when you start your machine. Turn off all the carp you find -eg open office quickstart, adobe updaters, asll thosde things which monitor printers, monitor for cameras, scanners, etc. This will save your system overheads (ram).
Now find (free) and install FREERAM XP PRO - that will automatically free up ram when needed, it also defrags your RAM (not your disk) and execute global memory compressions on demand or automatically, it also clears the clipboard (again saving RAM).
then with freeram XP installed you can see if you have any "memory leaks" from (eg. likely culprits - freebie screensavers, some java scripts, some beta programs, programs running macromedia flash lookalikes)
this works on all 3 of our workshop machines which, believe it or not, run XP pro on 256 of RAM, and on a "clean" system, including the one which runs the wizard, and the mat designer software isn't exactly a lightweight in its demands on the system
at home I have 2gb RAM, 6.8ghz dual core, and twin PCIE SLI graphics cards, liquid cooled, and overclocked the carp out of it, and I still use the above freebie progs to max the performace- but thats all to work flamethrowers in team fortress, hopefully you are too busy making frames to even think about picking up a virtual flamethrower
Thats a start!
kev