if you have a "naughty" version of cubase 5 then its a problem with vista and a certain piece of re-written code.. so we cant help you here

firstly if its genuine then it sounds as if your latency needs adjusting. put it up to 1024 and see what happens.

also consider using asio4all drivers instead of your soundcard drivers.

i presume you're using internal clocking unless you have an external clock? clocking isnt gonna be your issue.

it could also be a de-normalization problem with a plugin. try taking the plugins out 1 by 1 to find the culprit. after you've found it re-insert and place a dither plug in after it to combat the de-normalization.