Well, i found out how to clear the CMOS, removed my 9800, cleared the CMOS and reinstalled the 560Ti and unfortunately, this does not appear to have solved the problem.
However, i did track down the cause of the high CPU usage, namely system interrupts. I am currently trying to find out what is causing such a high level of interrupts, probably a driver, and will post this when i can.
the bottom line is that my shiny new graphics card is now back in my PC, which is currently running like an absolute dog.
Cheers