The following programs were found by a CS273 student in Fall, 2005, at http://www.ele.uri.edu/Courses/ele205/. I'm making them available to you; but be aware that (1) I haven't tried them myself so I won't be able to help you, and (2) we'll be testing code with the simulator in the CS department.
His comments on the software are:
Hi Joe. I just wanted to let you know I found a pretty good assembler and simulator for Windows machines. I imagine a lot of people will find it useful. Anyway, I attached the programs and their manuals. A couple notes for using the simulator: First, when it loads, make sure to tell it to start at address f800. Also, click on "M68HC11 CPU," "Browse Mem," and "Registers" to open their windows to watch the program run. It seems to work fine. I tested it on the program we wrote in class. I just made the file in a new text document and named it with the .asm extension, then to assemble it, just typed: as11 filename.asm from a command prompt. I hope this is useful for some people. It will be for me.