Query Help

Greetings:

I wanted to write a stored procedure that had somewhat of a dynamic query.  I wanted to pass it a string to be used in the "WHERE" clause. Here is a snippet of code to demonstrate my request:

CREATE PROCEDURE spTesting
    @Filter          varchar(255)
AS

SELECT      *
FROM     Table1
WHERE      @Filter

So for instance, if @Filter would be "FieldName1 = 'John'"; how would I do this?  So once the variable is passed the query would execute like the following:

SELECT  *
FROM    Table1
WHERE   FieldName1 = 'John'

Thanks!
-Jacob