If your HD is highly fragmented, defragging can buy you a little speed but probably not much. Killing as many extraneous tasks as possible is probably your best zero cost help. I think it's always a good idea to use Window's configuration editor or something like the freeware "RgeCleaner" to check your startup settings and remove any non-essential stuff from starting in the first place. RealPlayer and Quicktime tend to have little tasks always running for instance. I've used Real Alternative and QuickTime Alternative to banish both those beasts altogether. You might also try Fast Defrag 2 which will free up any unused memory. Sometimes killing or exiting a program doesn't free up the used RAM immediately. All these are freeware so it doesn't cost anything to try them.

"Democracy is a pathetic belief in the collective wisdom of individual ignorance." - H. L. Mencken