Yesterday I uninstalled a LOT of programs and deleted some files I don't need, that got me about 40-60GB of space
What you should do is start->execute type in msconfig and go to autostart.
Deactivate as much as you can.
This will give you more performance because you have less backround processes running.
At friends computers I have seen horrible things when I watched what processes were running.
I havent defraged for 2 years and I was also astonished when I saw my harddrives were completely fragmented.(I thought that doesnt happen with ntfs
Defragmenting the hdds brought a noticably increase in loading time. (cod4 maps)
defrag your ENTIRE hdd, overclock your CPU(if u have a 3rd party cooler),pray it loads faster thats about all u can do
There is no reason to overheat the cpu when its the ram that cant shovel the data in fast enough.
My cpu is overclocked a little but the advantage isnt so big, I just do it because its for free