Help With HP X4000, XEON speeds, FSB and Overclocking.

Okay, I bought a x4000 with two 2.0 ghz xeon processors on ebay a while back, now, I bought it as a cheap gaming system (I know, stupid...) But I popped in a GeForce 6200 AGP and I was able to run most of the games I want with ease.

Now, I'm not a major gamer and I don't have the money to buy/build a new system (as I really want to try overclocking a pentium D to 4.2 ghz...)

but I want to overclock or otherwise make my system run faster.

I was considering buying two of these processors

http://cgi.ebay.com/Intel-Xeon-2-8-...ryZ51055QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

or something similiar.. as I understand the HP can only take up to 400 mhz fsb?
I also understand it can take the tyran (sp?) bios so it can accept 3.0 Ghz processors?

My major question is, can I overclock the computer (even a little...) and how can this be done as HP computers are locked (all my googling turned up veyr little.)

Thanks for the help!