Hi Marr
I have had problems in the past doing this and still get the odd video file out of sync but most work ok. I use this software now and find it great.
http://www.vso-software.fr/products/convert_x_to_dvd/
I would make sure nothing else is running on your PC while doing this or run anything while you are converting it.
I usually do it at night and leave it to convert when I got to bed
Check the video file first in your media software to make sure it is in time before you start converting in the first place as this might be the cause!
Make sure your software that you are using to burn it onto DVD is also working fine.
Hope this helps!
Cheers,
Johnnyk