I used the new DVD2 (b)? the new released with bug fixes. For some reason it recompressed video I had already rendered in VV5. Have anyone else ran into this?
As bStro indicated, the template can make a difference. I think it will recompress if you included the audio when rendering in Vegas. Make sure you use the DVD Architect template (NTSC or PAL) which doesn't include the audio in the MPEG file.