Look for values in database.

Hi

i wonder if its a way to see if what a users put into the form already exist.
For example. if the user need to be invited, then he need to put in the inviters id number, and if it exist then he can do registration.

Do i need to do that with action hock? not sure ho that works..
i have created a text box. and in there i can put custom validate.

can that see if the inviter id already in the database?