A/V Sycn or Voodoo magic

[Riverpatrol]

Tools:
Smartripper 2.41
FlasKMPEG 0.6 (had to use a Deinterlace video setting of 3)
DivX 4.12 (build 307) 25 frames 496x384
Windows Media Audio V2 64 kbps, stereo (for audio/video)

Machine is plenty powerful Athlon 1.2 gig with frills

OK. I'm getting the chicken ready on this one.

I have no problem in compressing the video from the vob file and I'm quite happy with the results and I can also rip the WAV file, no problem.

The problem occurs when I use virtual dub to add the audio.
The real time length for the formats are:
51:22 video
51:50 audio

but when the job is finished I get a movie than reports a time of
56:26!!! and it's naturally horrably out of sync.

I have attempted the process on two different machines and it's the same result. I have read loads of posts and tips but I can't explain the added four minutes or so.

I have had lots of success with other rips and I've consulted a mate that does a bit but we are... stumpted.
I hope one of you could shed some light on this.
Cheers

PS: I find some movies have an audio bit rate of 128 but if I try that virtual dub reports: unable to initialise audio encoding. Any thoughts?

Thanks in Advance