In case of DVD lab (which supports ChapterExtractors files) watch this:
http://www.mediachance.com/dvdlab/Help/quick%20ger.htm
Its in german, but there should also be an english version avaiable.
Just go to the Chapter Settings and choose import ChapterExtractor chapters.
BTW. Capturing the stills is very Easy.
Open your 720x576!!! AVS in Vdub or Zoomplayer and move to a point which shows your wanted Image to choose as Background. You also can use any other player which shows your image in an non-anamorphic state.
Do "ALT+Druck" (german Keypad) and paste the image into a new generated Photoshop document. and safe it as Bitmap.
Using Photoshop because DVDlab supports Photoshop's layers!!!! = Amazing in case of Buttons etc.
You also can use PS for generating your own backgrunds (the ones shipped with DVDlab do look awful!!
. BUT be shure that the highest white point in PS does not got under 10%! If not you'll obtain clipping and in case of white typo this looks awful.