Reauthoring DVDs without re-encoding: Best Freeware / Open Source programs?

[video_brain_dead]

I'm a newbie at making home video dvds; consequently, I converted some old vhs tapes
to dvd-r's which came out fine but I didn't include any menus or opening / closing graphics;
whereas, the dvds just play immediately when you put them in.

Now, I would like to redo these and add menus and graphics but don't want to degrade the picture
quality by re-recoding.

I currently run WinXP, but have access to a Linux machine.

Does anybody know of a high quality Freeware or Open Source program that can help me?

Thanks in advance.

[guns1inger]

PGCDemux or DGIndex to demux the content to elementary streams ready for authoring.

GUIForDVDAuthor to create a new DVD structure with menus, chapters etc.

All free, and no re-encoding.