RegaRDING THE SOFTWARE:
Didn't your DVD burner come with a basic DVD authoring software app?
if you're keeping it simple(no motion menus etc), you should be okay with whatever is right out of the box (mine came with Sonics (DVDit LE, which if you're a Flash maven, will make DVD creation seem insultingly simple compared to a Flash site).

Capturing Screen activity:
I use a combination of a tv card with an analog in on one computer and a VGA output device attached to the video port on another computer, I manipulate the screen on the second in the tv window of the first while capturing. Technically it works, however, due to pixel shape etc, sometimes the resulting video is pretty rough.

Capturing Interactive TV:
Try hooking a DV Cam into the RCA output of the Cable(InteractiveTV) Box, and hitting record while you do it.

Any questions, email me at [email protected] and I'll send my phone number to you.