Which configuration would be better?

[andersonmat]

I would personally go with the P4 setup just because of the RAM that is included especially if you will be hosting a bunch of players! I know that my old dedicated server was always short on RAM when running multiple players!
The P4 should suffice to the current setup... If you aren't going to be doing a whole lot of hosting of players--then the Core2Duo would be good!

Hope this helps!

Matt