VDRs are not scripts - they are Frameserver Signpost files.
You create them by setting up how you want your video to look and sound in VirtualDub (filters, audio conversion, but not compression settings cause they'll do nothing) and then go File->Start Frameserver. You then save a .VDR signpost file which you can open in other programs (including another VirtualDub - this is useful for people with Dual Processor systems) and they will request frames which VirtualDub will then process and relay.
I would not try scripting one by hand, and also the file will stop working once you hit the "End Frameserver" or whatever button in the window VirtualDub creates when you start the frameserver.
VDR files are _not_ a scripting language similar to AVISynth, they are an extension of VirtualDub which allow piping its output to other programs.