I can't see an equivalent in Win_7 - has anyone else found it?In an explorer window > Tools > Folder Options > File Types > highlight DWG in list, > Advanced > highlight OPEN > Edit... > (If open isn't there use New.. to create it.)
check that - Application used to perform action: = "C:\Program Files\AutoCADversion\acad.exe" "%1".
check that - "Use DDE" is checked.
check that - "DDE Message:" = [open("%1")]
This is the closest I have found -