The difference in the expiry date bewteen WINVER and SIW has been bugging me -- I know it's a moot point since RTM will be out LONG before then but some things just stay in the brain.
Anyway the REAL expiry date is based on the Licensing procedure
so if you type in elevated command mode
you'll find the expiry date is (in my case) 02 june 2010 -- yours might be 01 June 2010 -- depending on regional code and when you installed it.
After entering the command wait a few seconds for a new window to appear.
So SIW has it.