OK thanks, I'll give it a try. The reason I asked about trying it without the CPU was that if it gave the same error beeps without the CPU, the fault could definitely be determined to be with the memory. Having said that, if the CPU was causing it, then a faulty CPU could give the same result as no CPU...
I've contacted AMD anyway and I'm going to RMA the CPU. They've been very helpful today and it's a major part I could do with having checked out. I know it's a pain in the arse, but even if they charge a testing fee if it comes back OK it's still cheaper than buying a new socket 754 board to test it in.
The PSU leads are all plugged in and fine by the way.