I tried with older binaries to discard a serious driver issue and the
change seems to be Nov 2006. The attached PNG shows the bound box
of a nurbs (top) and edit mode of a normal curve (bottom) plus the garbage.
Both types seem to be affected at the same time.

Selecting curves will trigger the bug, making all curves and nurbs vanish
until the program is restarted. Entering edit mode is ok if curve or nurbs
is already selected on load, you can move handles and all goes fine, you
can add other objects like meshes for example, but as soon as you select
any curve or nurbs all them will go away and rare lines will appear instead.

Thus the card and driver are capable of drawing curves, as they are ok just
after start or after the first added curve, but something later makes the
program misbehave.