>I have SQL Server 2008 64bits R2 and I need to install SP1 on top of it. However, when running the install program, it gives us the following options:
>
>New installation or add features to an existing installation
>Upgrade from SQL Server 2000, SQL Server 2005 or SQL Server 2008
>Search for product updates
>
>So, nothing in there mentions something about SP1. Which one should we choose?

I think you made the same mistake as I initially did and downloaded the wrong file. I also got this prompt first, then look closer in the downloads page and downloaded the right one. I think I even posted about it in the comment to Glenn's blog.