I'm not sure you can burn with iDVD or DVDSP from a VIDEO_TS folder, I use Toast for that, any good burning utility should do, but toast 6 works well. I archive DVD projects like that all the time.
If you need to be able to edit you DVD's later you can't create a VIDEO_TS folder, you need to use the "Archive Project" option from DVDSP, or simply store the MPEG2 and audio files (muxed if using iDVD)and the graphics stuff along with the DVDSP file. This is much more economical with space than storing 2 hours of DV-stream and render files from a FCP project.
You can also save an iDVD project by unchecking the "delete rendered assets" (I think...) from the iDVD preferences, apparently this saves the converted video/audio as part of the iDVD file, and you won't need to re-render when you burn, although I have never tried this.
You can always recover your video and audio from the VIDEO_TS folder using DVDX 1 to 1 or suchlike, but its time consuming and a pain.