Im trying to split a divx movie using virtual dub, into two halfs, so i can make a vcd out of it

They way that i've been told to do this, is to select the first half of the movie, and delete the rest
then save it out as a avi again

OK no probs for the first half of the movie
but when i do the exact same thing to the second half
(selecting the first half and deleting)
the video saves properly, but the audio is WAY off
its not cutting the audio at the correct place or something

any ideas?