If you want to use Regular Expressions, here is the link to a regexp that validates URL syntax.

http://regexlib.com/REDetails.aspx?regexp_id=146

>Hi - I have a customer form that enables a user to enter a website address. I want to check that the basic structure of the entered text is OK. I don't want to go off onto the internet and check if the address actually exists, just the basic syntax of whatever has been typed. Does anyone know of a comprehensive set of checks I can do to test if the URL is valid.
>
>Thanks