How can I create a DOS variable with a VB script variable? One that will only exist during while the program is running.

You cannot run a VBScript to modify an existing environment. If you wish to pass a value to the starting CMD, run your script from CSCRIPT.EXE, and pass your number as the ERRORLEVEL (via: WScript.Quit <number>).

Actually you can, I've found the problem seems to be that when you create the environment it gets deleted once the application closes. When I save a variable to the "USER" environment it only appears once you exit and start the command-line interface again and of course gets saved permanently. Until you have it deleted. I really don't have a clue other than redirecting the output to a file which the batch file picks up on and creates a variable from. Which to me, isn't exactly all that safe.

Actually you can, I've found the problem seems to be that when you create the environment it gets deleted once the application closes. Alright, you got me. you can't modify an existing environment that's not your own (you = any application). Any child application you spawn will inherit your modified environment, but your parent application's environment will remain untouched.

So my "solution" is the only one unless I do the entire project in VBS?

Yeah. The only thing returned to the parent process will be the ERRORLEVEL, returned by WScript.Quit. Or you can have your script launch a Command Script, and THAT will have your modified environment. (Assuming you modify the "PROCESS" environment.)