Redirect If Record Already Exists

I'm wanting to do a simple controlled voting page. I too our webserver off anonymous and everyone who accesses the website is a domain authenticated user. I've already done some control structure pages based on Request.ServerVariables("AUTH_USER"), which works great. That's also how I would do this page, in my basic thinking.

My idea is to have an access database with two tables. One table will have the vote written to it and the other table will have the AUTH_USER written to it when the employee casts their vote.

I'm wondering how I would do a test against that table to see if their name has already been written to the table. So, if an employee votes already, when they go to vote again, their user logon would be tested against all entries in the table and if it exists, the vote would not be written and they would be redirected to another page that politely tells them they've already voted.