OT: MacPro is playing up - any tips?

[David Bovill]

Today my MacPro suddenly decided to freeze - with pretty green stipes and
pink squares all over the screen. Restarting only worked after resetting
PRAM and rebooting in Single User Mode. It's been a very long time since
I've had a problem with an OSX machine - so I am wandering if there are any
diagnostic tips out there? If feels like an Xwindows / video card issue -
but I am wandering what steps I can take to help diagnose the issue?

Thanks in advance :(