If everything is legal, why don't you install SP2, you have nothing to worry about. With it's background intelligent transfer (BIT), it will install itself and then remove all unncessary files.
You could also use your disk cleanup tool to remove all unnecessary junk. (If you haven't used this in a while, you might be surprised at how much junk, that can pile up.
Then you should defragment your hard disk to have everything nealty set to install a program. You could also go and get Tweakui from Microsoft and go through all the points to maximize your system efficiency. If you have two drives, you should have your swapfile on the drive that is not occupied by the operating system or windows, and should set you swapfile at 1.5 times the amount of RAM your system have and set that value for both minimum and maximum to limit fragmentation.
you can go to http://www.pureperformance.com
for more tweaks.