As noted above, Vegas uses two different capture programs:
"External" for DV,
"Internal" for HDV.

When you first try to capture in Vegas a dialog is presented that allows you to choose either one, and also a checkbox to always use that choice.

If you no longer see that dialog when selecting the capture function, go to Options | Preferences | Video and reset there.

Capture HDV
 

I finally solved it by doing two things. First in 'preferences' I unchecked the "Use External Capture device; and second there is this little button at the top left of the window trhat is for "capture preferences." On that you set your capture device, and it should pop right on; assuming the camera is already turned on and feeding HDV@60fps.