Patch - keep in mind that the E8400 is nearly 5 years old already, and your PC is much much older. We are not helping the OP to build an old computer here ;) Today's parts performance and compatability are quite a lot more, whereas back then most CPUs and mobo's did support DDR2 memory, where the popular FSB speeds were 667MHz or 800MHz. Obviously if you had those components you couldn't get brand new super-expensive DDR3 memory (wouldn't fit in the mobo), and it would've been pointless getting RAM with an FSB speed greater than your current weakest link in the FSB (667 or 800MHz).
1. Most mainstream components (at least where I am) have a similar FSB speed these days (1333MHz and up).
2. The OP is on a budget, so it's unlikely any of the parts he choses will be too fast for the rest of his NEW computer anyway. ;)
If you have more questions patch, feel free to PM me.