Additional Info:
I just deinstalled the V7 and installed V6.6a (64bit) and opened an older file, that was not created or saved under V7 before.
Same problem with weird lines in the 3D view...

One "simple" question:
Is that bug only with AMD cards, or is it known also with NVIDIA graphics?

In other words: If I install a NVIDIA card, should it work (with V6 and V7 and 64bit installation??)