Hi,
The Retail dvd you normally buy is for use on one pc - you can move it to another, but only supposed to be on one at a time (it is possible to buy licenses for multiple machines-but for your average person getting it from Newegg etc, it's one pc ). You also get support i.e you can ring/email M$ for free help.
The System Builder (sometimes confusingly called OEM ) dvd is identical - the media is exactly the same. However, you don't get free support (do you care ?). The difference is the license. Sys. build are for one pc also - but only supposed to be for the pc they were first installed on. You can reinstall as often as you like on the same machine - but are not supposed to move it to another.
They are almost half the price.
Upgrade dvd's are slightly different. You need to install them from within Windows - they need to recognise an existing qualifying windows installation, before they go ahead. Since they overwrite the existing install - you effectively swap your existing o/s for the new one. You are not supposed to keep both running.
It is possible to do a clean install with upgrade dvd , but it's not in the spirit of the thing and in any case it's a hassle to double install it each time.
IMO Sys build is the one to go for unless you plan on calling M$ every 5 mins.
Pricing for 7 is not announced , but you can bet it will be more than Vista was. Interesting to see if they give a good deal for the upgrade dvd from Vista to 7.
SIW2
Hope that helps.
