well since your not gaming then that will save you about 100 at least
Basically if you installed the stuff yourself(or got a mate to do it) you could have a new processor and 2gigs of ram for between 200-250 depending on what spec processor you buy.

A decent case could be had for about 50-100, agian depending on what one you pick.

I use this site http://www.ebuyer.com/customer/home/ to get all my pc bits

By the way what pc do you have at the moment?(depending on this you might be able to keep the motherboard but if its too old/wrong type for a new processor then you will need one of those too) but for what you want you wont spend anywhere near 500