Right, this happened a few times over the past few weeks.
Basically it would start with Vista becoming sluggish then crashing. Upon reboot varying things would happen, but the same drive always flagged up. Managed to get round it before with random ways till last night when it reset itself as a non RAID disc.
Anyway, changed it to RAID 5 and used Ghost to put my OS back on, marked it as normal and the array has been re-built and it all seems fine again (RAID 0 before).
I still can't get into WDLGT, should I call WD and see if they will replace the drive?