What does your DGIndex template look like?
It's not required to have the full path, because AviSynth and DGIndex both accept relative paths (in DGIndex you have to turn off full paths, but AviSynth accepts them from the get-go). As long as the script and .d2v are in the same folder as the video, you won't have any problems omitting the full path. You just need the filename if the script is in the same folder [AVISource("testvideo.avi")], or the relevant information to get from the script to the file, as the case may be, such as AVISource("testfiles/testvideo.avi").
If DGIndex is indeed messed up (i.e., the template doesn't have "__vid__" where the .d2v normally is), then add it in there. You'll need to go into DGIndex itself, and manually select the template file afterward. Options->AVS Template, Change Template File, and give it the template.avs file residing in DGIndex's directory.
To quickly copy filenames or full paths, take a look at
Ninotech Path Copy (for XP; dunno if it works in Vista). Also note that it's a 32-bit shell extension.