Pop-up

I have a form, but not submitting anything to the database yet. The person should be able to type in a username in the field called username and click the button to the right and it will check the Database to see if the username is valid...The problem is, I cannot get the username to pass to my other pop-up window. Is there someway I can validate what is already in the database and then pass it to the pop-up window? Or, is there someway to pass the variable to the other page, and give an error if already in use? I appreciate the help! (i.e print "<TD COLSPAN=5><INPUT TYPE=TEXT NAME=username>"."&nbsp;". "<INPUT TYPE=button VALUE=Check! OnClick=displayWindow('error.html',300,300)>"."&nbsp;Check for valid user-name"."</TD>"; ) Thanks. bryan