updatepanel

hello!
is there a way that a control outside the updatepanel can read the content of a textbox in the updatepanel?
because i want to create the create wizard of a user so i want for the username an updatepanel so i can refresh only this updatepanel because i want to be sure that this username is unique,and an updatepanel for the 2 textbox for the password,and others,so i want at last to create the button of submit so i can make sure that all the field is filled and to take this values and insert it in database,so the button and the different textbox should be in different panel not always to refresh all the pages.
thank you very much for your help.