On www.plextools.com, but it's not released yet. Theoretically, a video dvd is just a data DVD with some restrictions. I'm not so sure ordinary Plextools can't do it (but not sure it can either...). VIDEO_TS must be the first directory on the disc, all VOB files must be stored one after another on the disc and all less than 1GB in size, and the disc must support the UDF file system.
If the standard Plextools allows you to control this file ordering, it has all you need for the basic disc creation. If the files are not in the right order, PCs will play them, but set-top boxes won't.
Someone out there please comment if they've tried this.