jeffreyh:graemeh: I upgraded a beta unit I got off Trade Me to 1TB and had no problems at all. The green WD drive I got from Ascent worked perfectly and is ever so quiet :)
Was this the internal drive? and was it much problem?
Yes it was and it was no problem at all. The copying of recorded content from the old disk to the new disk took a while though and I had to buy a SATA card for my PC because it's old and only had IDE.
I used the method where you burn a boot CD running linux and then run a special program. You can do it from Windows too but I didn't trust Windows to not do something stupid with partitions or otherwise mess with me.
There was also a program I had to run that was specific to the WD drive to change the sleep timer on the drive. If you want me to dig out the instructions I used let me know but they are easy enough to find with google.