Shouldn't be necessary, as there's no copy encryption (unless you are using them to burn the DVD.)
"VTS_01_0.VOB 25mb (BitComet Incomplete Download File)"
Is this the warning that the software is giving you? How do you know it's incomplete?
Anyways, have you tried playing the DVD files by loading them in your software player? If they work, then you should be able to burn the files as they are. What kind of problems are you having, specifically?