You could hook into Windows to press and unpress keys, but it is probably more functional to use INSIM. Full documentation is in the LFS\docs folder in the file called insim.txt (You would send an MSO struct with the command in).
Both methods are advanced concepts, INSIM probably requires a little more understanding of streams and network sockets but if you are using vb6 you're used to doing things the hard way anyway
To find the windows function calls for the keypress method you will need to know how to hook a .dll in vb6, then its just a matter of knowing the decorated function name and parameters for the function which are all on msdn.