Well... Ndisasm will disassemble it, but that doesn't give you sourcecode. Maybe look for "sourcer" or "IDA Pro" (an expensive commercial program, but there's a free trial version). Not much information to go on in a .com file. You might find it easier to write something from scratch that does the same thing... or something different - you've got the executable, no point in having source code unless you want to change it...
What's the program? Something "available"? Perhaps more important, what's the licence? This is "illegal" (amazingly!), and I don't think we want to discuss it here, unless the licence permits!
Writing duplicate functionality should be safer - I think the "look and feel" lawsuits are gone... (?)...
Best,
Frank
