You can go back to Vista at any time by means of a clean install.. All you have to do is put your Vista disc in and boot off of it than do a clean install.. However, I wouldn't worry too much about the RC expiring as the Retail (Final Version) of Windows 7 will most likely be released prior to the RC AND RTM's expiration date's.. In other words you'll most likely be able to purchase Windows 7 long before the RC expires..
But yes you can go back to Vista at any time if you so choose... Just remember to format the partition that contains the Windows 7 RC before you install Vista..
No, it's not a software update, it's the entire operating system. When you upgrade from Vista to Win 7 there is nothing left of the Vista operating system to go back to. You'll have to save your data and do a clean install of Vista.
But, by the time the RC expires next year you should be able to buy an upgrade license for less than $200. Even an OEM copy of Vista Ultimate is only about $180 right now. Besides, 1 year is plenty of time to save up $200-300.
Hi -- by an "Upgrade price I mean that so long as you have an existing VISTA license you'll be able to purchase an "Upgrade" version of W7 at a cheaper price.
You'll still be able to do a clean install -- it will merely ask you to run the install.exe file from within an existing VISTA installation. At the prompt you can select CLEAN install (New install) or upgrade.
Its only if you purchase vista I think the date is June of 2009 that you will get a free upgrade to Windows 7. The date could be tentative.
Deleting an os within an os sounds like your explaining internet explorer 8 where you can delete the beta and you would have internet explorer 7. My guess is you would need to clean install with the vista image depending on your bios.