
These days desktop storage is cheap. True, now standard size is 500GB if not more. However, if you like where I'm at, some users are notorious for abusing the space. Not too long within a year their desktop is chewing up all the spaces with undisciplined manage on the users part. Having too much information leads to fragmentation and inability for Windows to perform page file (swap file) efficiently. Let me show you an simple commandline that could quickly free up between 1GB to 4GB of free space. Assuming you have SP1 that is the first thing I would do is to remove the SP1 one Un-install cache files. If your computer ran fine for the last few weeks after SP1 upgrade...I would say it is safe to remove them if you have no reason to keep them.
To remove it properly.
1. Login as an user with "administrative" rights.
2. R-click on the "Command Prompt" shortcut in Tools-->Accessories, then RUN AS ADMINISTRATOR. This is to force admin execution.
3. Now in the commandline type this in:
Prompt> dism /online /cleanup-image /spsuperseded
Hit Enter to execute. You should see something like the screenshot#1 below.
To remove it properly.
1. Login as an user with "administrative" rights.
2. R-click on the "Command Prompt" shortcut in Tools-->Accessories, then RUN AS ADMINISTRATOR. This is to force admin execution.
3. Now in the commandline type this in:
Prompt> dism /online /cleanup-image /spsuperseded
Hit Enter to execute. You should see something like the screenshot#1 below.
If for some reason it has already been removed you will get an error shown in screenshot#2.

For Windows VISTA, use this command at the command prompt:
Prompt>> compcln.exe