I have been having problems regarding audio/video sync when creating DVD file structures to hard disk using VideoStudio 8 and MPEG 2 files. The problem occurs when creating DVDs greater than 30 minutes in length. Nero 6.6 will create the full length DVD correctly using the same MPEG 2 input.

The DVDs start off in sync but at particular points, a small sync error is introduced, each one accumulating the time delay. If I use the same input MPEG 2 file and create a DVD of no longer than 30 minutes in length, everything stays in sync (the length varies from 28 - 34 minutes depending on the input file, but is consistant to the second for each particular file). Build a DVD even one second longer than the 'good time' for a particular MPEG and all sync errors are included, build it one second under and everything is perfectly in sync. This can be recreated time and again.

I have noticed that the 1Gb VOB files produced by Nero are all exactly the same size, and the same applies when I look at commercial discs (although it differs slightly from disc to disc). The VOB files created by VideoStudio are all around 1Gb but each one is slightly different in size.

Does anyone understand the DVD file structure enough to identify if the problem lies with the length of the VOB files (and therfore VideoStudio 8 which is creating them)? I have read the document on the DVD File structure but it doesn't contain enough information for me to identify if differing VOB lengths could cause the problem.

Nope. it's not VS8, it's Nero.
Nero's encoding engine is well known for creating audio sync issues. It doesn't transcode to 48khz properly.
Use a better encoder like Canopus Procoder, Mainconcept, CCE or Tmpgenc.
Your alternative is to use elementary streams (actually recommended).
Encode video only in one of the above encoders. Transcode audio to AC3 48khz in Ffmpeggui, and mux the two in your authoring app.

VOB sizes vary, depending on how the software reads what a megabyte is.
If it decides a meg is 1024k, the vob is a bit larger. If it decides a meg is 1000k, the vob is a bit smaller. Poorly written apps will use 1000k. This still falls into dvd spec, but is not really correct. As long as the vob is between 1000mb (1 gig) and 1024mb (1 gig) it should be fine.