Dave, see if this technique from Gary James on the Sony Vegas forum works for you.
Make sure you’ve copied the VIDEO_TS folder and it’s contents to your hard drive first.
Vegas allows you to open up a DVD .IFO file. This imports the entire .VOB chain for both video and audio tracks.
Click File / Open, then navigate to your VIDEO_TS sub directory and enter *.IFO in the File name input field.
For a regular DVD you will see a VIDEO_TS.IFO, and a VTS_01_0.IFO.
Select the VTS_01_0.IFO file and click on Open.
Don’t try this on a DVD disk because Vegas will try to build an .sfk file containing audio peaks in the VIDEO_TS directory.