Starting my Program by double clicking a text file

i have been using vb.net system.environment.commandline to determine if my program was started by double clicking a file with an extension .xxx or if my program's .exe file was opened. if the program was started by the .xxx file then the commandline value would have a .xxx extension.

the problem is when i use xp everything works well, but when i try to install it on a 2000 server machine the commandline is always the same, the .exe location.

i have tried using the system.environment.currentdirectory but it doesn't return the exact file path.

any suggestions....