>>>I did a search on Amazon and found out that they sell SQL Server 2008 Developer Edition. If this is not the latest version, will I be able to update it online? That is, do you think it is ok to buy it on Amazon?
>>
>>I think you can install R2 on the top of SQL Server 2008. I tried to confirm it yesterday by asking on the developers forum, but nobody replied.
>
>What is R2? Is it like SP2?

It's more than a service pack and less than a full blown new version. More info here --

http://www.brentozar.com/archive/2009/09/sql-server-2008-r2-frequently-asked-questions/

And LOTS more info here in a free e-book --

http://blogs.msdn.com/b/microsoft_press/archive/2010/04/14/free-ebook-introducing-microsoft-sql-server-2008-r2.aspx