I have a Nikon D50 and a Televid 77 Angle. What do I need to use the Televid on the Nikon? What is the approx. focal length of the Televid used as a lens. Thanks.

Not sure of that scope ...

But the cheap option may be a
"T2 to Nikon adapter"
The T mount is a flange for the camera with a screw thread inside so then you use another adapter that's the eyepiece for the scope. T2 is a 2 part one that you can turn so the camera is the right way up.

I'm sure Leica make something much nicer but It's probably not cheap!
there you go ...
http://www.company7.com/leica/televcam.html