grafics cards

[Mr_P]

it's Mac Os X 10.6.8 on a mac Pro. I've read on this forum that 10.6.7 offers no advantages

I think you mean 10.7 - (10.6.7 would be a downgrade...)
Most new MacPros are being delivered with 10.8.2 - which is fine - but still possible to downgrade to 10.6.8 if required...

I'll upgrade to the latest Nvidia drivers. Things seem to have settled down (Catalyst made it through last night). The green lines problem was cured by forcibly installing the individual Nvidia drivers (the package installer said they weren't required).

Bit odd - never seen this problem - usually the drivers are a simple install?
Did you get a picture of the green lines?

Catalyst version is 4.40_m364_HD. Am I using the most appropriate version of Catalyst?

m364 is the current public release and necessary if using 10. or 10.8 - but also works with 10.6.8

S