Stutter, jitter and then, not?!

Hey folks,
i've started building my project and it was all ... not too performant. but i didnt bother because i didnt optimize or anything at that point so it was expected not to run smooth... now after optimizing it still stutters.
now the weird thing: it only does so on my main machine. it runs perfectly fine on my notebook, which is considerably less able in terms of processing power.

so here are the specs

Main machine:
core2duo 2.66ghz
4gb ram
gforce7900gs (7950gs?!) + latest driver installed

Laptop
core2duo 1.66ghz
2gb ram
intel gsm 945 express, some elder driver that still supports opengl (the newer ones doesn't, like, at all)

both systems run win7x64

how the stutter appears:
with opentk1 rc it appeared very slightly at about every second
with opentk1 b3 it appears as frequent as before, but more intense.

renderfrequency outputs around 60fps,
updatefrequency is well in the thousands.
vsync is on, but off does the same.

thanks for your support!

regards

wzl

Edit:
the same appears in the example binaries, so i'm assuming its either something with the driver, some setting, or something OpenTK internal.

Edit2:
I did some more research on this
htt p://gpwiki.org/forums/viewtopic.php?t=9845

and everything pretty much points at nvidia's drivers. But knowing that, doesn't help me too much.
I'll keep you updated if i find more information.