A tip for anyone who might be entering into the same kind
of bummer I just went through:
When I first got Vegas Video I spent a couple of weeks in
utter frustration... DV clips that went "in" fine, came out
unusable when rendered, when I tried to send the result
back to the camcorder. The rendered material would start
out fine, then break up and go to random stroboscopic
effects. Went back & forth with SF tech support about
checking my settings, etc. etc.

Long-story-short is: I finally determined that the problem
is my brand-new "high-speed" 30-gigabyte disk. The @*#%
thing isn't fast enough to feed the video stream smoothly
back to the camera. Confirmed this by clearing a couple of
gigs of space on my smaller, old hard disk, copying the
rendered file to that disk, and going to the camera from
there. Works fine, every time.

I hope this note may help someone short-circuit the
frustration process in case you encounter similar symptoms.
-Ernie