Install Books online only for SQL 2008 (Katmai)
Few out there are still not comfortable to install or test the SQL 2008 (Katmai) CTP as SQL 2005 is still 'fairly' new in the field and users are getting eventually hands-on experience.
So in order to get to know more on the documentation 'only' for SQL 2008 (katmai) then you can download the documentation files for a better understanding. Review SQL2008Bol download link (Microsoft suggests that - Do not attempt to download the binaries in this section until you have first registered into the SQL Server 2008 CTP program.)
Registering with Connect or signing into Connect does not automatically register you into SQL Server 2008 CTP program. You must in addition register by clicking here.
Also SQL2008ReadMe and June CTP Installation Requirements for Installation procedure and caveats to avoid.