Have you tried playing the converted dvd on the computer, prior to burning? If there is an audio/video sync problem in the video before burning to a disk, then you know for certain that the conversion process isn't working properly. If it only occurs after you burn, then something truly weird is happening in the burn, or is due to using crappy Memorex disks.
If you don't have dvd playback software, use VLC. www.videolan.org
I've never heard of ImgBurn not working on XP Pro. You have some issues somewhere in your system.