Value Checking

Okay I want to run a query against the DB to see if a new user is trying to take the name of an existing user at the web site. The users are placed in a members table in a MySQL database. How would I run a simple check like this on the DB. I understand the if...else part that I would need to write. If the User matches an existing user return to previous page else run this insert script. But how would the code look for the checking query? Thanks Phillip S. Baker phillip@wordsandimages.com Words & Images 1535 Seabright Avenue, Suite 100, Santa Cruz, CA 95062 Direct Line (831) 420-2641 / Fax (831) 458-0808