Givining permission to the bin file isn't going to be sufficent -- as a pratical matter, you'll need to give ASPNET user permissions to run Microsoft Word, and probably more than that besides. For example, it wouldn't suprise me in the slightest to discover that there are three or four .DLLs that you need to grant permissions to in the system32 directory in order to make Word start up properly. It sounds like the filemon will enable you to work out (eventually!) which files you need access to.
Of course, the real question is "How long will you with the 'minimum security privilages' model (by adding permissions one file at a time to ASPNET) before you give up and grant ASPNET local adminstrator privilages, security be dammed?" :)