OK, the first step is to create a recordset that queries your existing users table to check the email address column for the email addrress that was entered into the registration form.
This is a strait forward recordset that can be created in Simple View, Select the old usrs table, set it to return all columns, in the filtering section, select the "UserEmail" column "=" "Form Variable" "UserEmail". name the recordset "emailLookup"
The next step is to edit the server validation server behavior.
In the server behaviors list, double click the server validation server behavior.
from the list of validation types, select number validation.
for the server variable, enter:
click the plus button to add it, and set the minimum number to 1.