If you have MPEG Streamclip, you can open a movie in its VIDEO_TS folder, then perform a "Convert to MPEG" which rewraps the transport stream into a program stream file with a ".mpeg" suffix. Do that with your second DVD too. You can then burn both to a DVD using Toast. I have Toast 8 and I drop MPEG files onto Toast in the "Video -> DVD-Video" section and then burn away.
Note: the total file size of both movies needs to fit on one blank DVD or Toast will have to re-encode the videos to fit them on. You don't want that to happen.
Note 2: of course you need Apple's MPEG2 decoder component on your system for MPEG Streamclip to work its magic on MPEG2 files. I assume everyone has it, though I understand that's not always the case.