After an update to XP SP3 it could be that your Windows directory is full with the backup files that are not deleted after the install completes.
You can safely delete any folder under C:\Windows\ that begins with "$NtUninstall", the only side effect is that you will not be able to revert back to SP2 or whatever you have before. This can save a couple of hundred MB (maybe).
A tool to delete these files for you is XP Remove Hotfix Backup
Another thing to do is make sure system restore is disabled which could also be taking up space. The downside here is that you lose the ability to restore previous settings, which IMO was near useless in XP anyway.
Other than that run disk clean-up and make sure that all temporary files get deleted.
Deleting things like IE, Windows Media and others, while they are apparently useless to you will at best impair certain functionalities within Windows such as thumbnails for video files, Active Desktop and some other items. I wouldn't recommend trying that unless you really know what you're removing.