Two words: TIME STUDY.

We use them where I work to determine budgeted hours per department. (I work in a manufacturing plant where I am the lead in a particular department). Basically, you would just have to put together a spreadsheet of your tasks in the IT area and the time it takes to complete such tasks (server maintenence, hardware support, support tasks, etc.) Add up the total time for your IT responsibilities, and subtract that time from the hours that you are expected to work each day (8-10 hours, I suppose). Do this few times to establish a variance on the necessary time for your primary responsibilities, and present your findings to your supervisor. Whatever time is left over, is time that you could spend in other departments. (Don't forget to include your break times in the calculations). Hopefully, your boss will see that your "free time" is so sporadic and inconsistent that it would be useless to try to force you to take on sales tasks as well.

Make any sense? Hope it helps or at least gives you something to ponder.

O