ok.... from your advice I did the following checks...

Memtest+ overnight completes 17 cycles error free. The ram timings i left on overdrive 'turbo' setting in the bios: simular to manually tweeking the timings.

Did a burn in test with Sandra - only errors that came up pertained to the CD roms/Floppy that it was trying to read/write to. Some had no disks in so I recieved an error message saying so. The Radeon card got the error: "Required display format not available. Try updating the video drivers".. Memory again passed this burn in on Sandra.

Checked My Raid Array which is about 250gb on raid1 (not stripped but mirrored) over 3 disks. A-OK

Checked temps of PC in general using sandra over load playing EB. All pretty rock solid and nothing over 55 degees C. At idle the Radeon was around 33 degees C. All voltages were rock solid with slight rises in areas when playing EB.

Any ideas where to go from here....?