Look in the help file under "File Commands" for "Execute File". This allows you to shell execute another file, and also allows for command line switches to be added. Returning information from this external program is a bit more difficult, the fastest way probably being to have the program create a file, then read it in your main program. Please note, this may not be the only way to communicate with external things, it's just what I could come up with in 2 seconds.
System Specs: AMD Athlon 1700+ XP, GA-7VRX motherboard, 128MB DDR RAM, GeForce2 MX400 64MB VRAM