I'm currently planning to purchase a server for our MySQL database. I'm deciding whether to get an Intel 2 x quad core Core2Duo processor or 2 x dual core Xeon. Any feedback will be appreciated.
There are no quad core processors in the Core2Duo line. The quad core line is Core2Quad, and you cannot put more than one processor on the same motherboard from that line of processors.
A good quad core is the Q9550 aka X3360 which runs on LGA775, only one per motherboard, but if you want to get more power from a single quad core you can go with an X3460 which runs on LGA1136 motherboards and requires DDR3 RAM but is faster than the Q9550 even though the clockrate is slightly lower.
Setting up 2 dual core processors seems like a waste of cash, since you'll be paying for both the processors as well as a motherboard with 2 sockets instead of a single processor and a single socket motherboard.