The socket on the motherboard is a 775. I checked out Asus' website for a list of CPUs. It only lists Single/Dual core processors, but seeing as how the processor is 5-6 years old, and Asus has a gajillion newer MBs, I suspect that the list is heavily outdated.
Would there be any chance that a quad core CPU would work on this MB? Or some processor that isn't insanely priced (£400 for a Core Extreme? Yeah right.) and delivers good/great/best possible performance with price in mind? Would any 775 socket CPU work on a 775 socket MB?
Sorry, but it's a motherboard with a 945 chipset and it doesn't support Quad Core processors (they draw too much current for that motherboard). The CPU list is accurate. You could buy a used motherbaord that supports a Quad Core, but building a new PC based on current technology would make a lot of sense.