I just bought FM 11 and can't share either. I made sure to ask the sales rep about it prior to buying and she said it was "easy". Not so I find. Seems like this is a common problem. Does anyone have a solution?
The sharing option itself should be there in the File menu unless someone's done something cute like installing a custom menu that omits it. You will see a few differences inside the sharing | filemaker Network dialog depending on whether the file you have opened is local to your machine or hosted elsewhere, but that doesn't seem to be what you are describing here.