[unit91]

I'd go to your boss and respectfully say what you've said here regarding your interview and intentions. "Sir/ma'am I was hired to do job X and I find myself doing job Y. Is job X still a realistic goal here? If so, when do I start? [a date should be the response]. If not, I'll start looking for job X. I don't want to burn the company, so I'll continue to work hard here until I find the job, and I'll keep you posted on the progress."

Some folks might say "no way dude, they'll can you" but I doubt it. I think most bosses would appreciate the honesty. And if they do you wrong, you still have your integrity and that's better than one more paycheck.