Comparing a md5 encrypted username to the datase

[eluser]Bianca Migueis[/eluser]
Hi,
when people log in at my website the code encrypts their username with MD5 and stores it into a cookie and at the same time it updates the database with remember_me=true where 'user'=$user. My question is... later on how do i compare the MD5 encrypted user with the database? I basically want to find the place in the database where the user is equal to my MD5 encryption AND remember_me=true. I can't figure out how to do it except by returning the entire user database, encrypting all the usernames with MD5 and THEN comparing. Is there an easier way to do that?

EDIT: Should I create another field in the database to store the MD5 version of the usernames?