Upgrade Optiplex 330

Hi ! I recently found a Optiplex 330 and i want to upgrade it. The actual CPU is the "***" Intel Celeron 430 (1 Core @ 1.8Ghz) Yes, 1 Core..

Anyway, i need informations about the best processor i can put into this machine. I see on the manual of this computer only 1 or 2 core processors (Pentium Dual-Core, Celeron Dual Core or C2D). I need to know if i can put an decent C2Q.

I think the Q8400S is a good idea but i don't know if it works. I'm not rich, i can't buy a lot of CPUs for testing.
My BIOS is A11 (Latest) but I think DELL on this release "block" the possibility to put a Quad Core Processor inside this computer. I don't if it's true or false

Thanks for reply

PS : Sorry if my English is bad, i'm French