Try to get Adobe to render a single, multiplexed file. That's the simplest way and should keep the audio in sync.
Otherwise you'll need another program to multiplex the two files and worry about sync slippage. NeroVision Express 3 will do this.
Because of bugs in Nero 7 and NeroVision Express 4, I'm sticking with Nero 6 and NVE 3 so I can't advise you about the newest Nero versions.
Fav quote - "Experience is whatcha don't get 'till ya don't need it no more."
System - Athlon 1.4GHz, Win98, Hauppauge PVR250 receiver and compressor.
Software -Magix Movie Edit Pro 10, Nero 6 + NeroVision Express, Moho 4.61, PSP 8.1, Bryce, Quicktime 6.52 pro, Goldwave 5, DVD-Lab.
Cameras - Panasonic GS9, Canon ES8400V, Canon EOS D20 and Canon A70