Vista - Split location is unreliable

I'm importing video from a Digital-8 camcorder in AVI format. I want to split
a clip at a certain location, using the forward & backward buttons next to
the "Play" icon. However, the actual splitting can often take place a second
or so away from where I specify that it should take place. The buttons also
don't work reliably, e.g., 4 steps forward followed by 4 steps backward
doesnt bring you back to the same location within the clip.

I'm using Vista with all the updates. My PC is 2.13Ghz in speed, with 2GB of
memory and plenty of disk space.