A normal user will use no more than 20% of the options that Windows XP has (which occupy a lot of space on your hard drive), and this is what you can avoid with a tool like System Restore Control 1.0. It will compress the majority of options that are not normally used, creating more space on your hard drive.
The program does compressions after certain intervals (which can be regulated by the user) and you can always return to the original state of the computer or restore some options if they become needed.