It is probably a dependency on the C runtime library.
Have a look at
msdn and see if you can get anything from there. I think the free version of Visual C++ 2005 is missing some of the redistributable directories (whether by accident or on purpose, I am not sure).
You may be able to just copy the msvcr80.dll into your program's directory on your friend's machine.
If you can't get it to work, I can give you a manifest file to use (its at work, so I can't get it until tomorrow). The manifest file basically tells the program where to look for the runtime library DLLs.