Never the less and to confirm what Howard is alluding to, the older versions of NEWID() where TYPE 1 GUIDs, which were guaranteed to absolutely be unique provided there was no duplication of MAC addresses ever.

That is no longer the case in SQL Server. MS changed to a TYPE 4 GUID for NEWID() quite some time back because of the security aspects of being able to reverse engineer the MAC address from the TYPE 1 GUIDs. TYPE 4 GUIDs are nothing more than a pseudo-random number with a couple of reserved columns (one is always a "4" to identify the GUID as a TYPE 4 GUID). Even though there are a HUGE number of possible GUIDs (if each GUID were a mile long, the domain of GUIDS would span 14 Quadrillion Milky Way galaxies), even MS states that TYPE 4 GUIDs are actually NOT guaranteed to be "globally unique".

I'm also unsure why you would need to convert them to INTs (BIGINTs would actually be required) to confirm uniqueness. Just add a unique index to the column (as you should) and call it a day.