Iam not finding jack about this on the net. Can this be done in Reports designed in Report Designer or must you use other components such as Report Builder I hope it's not just limited to Report Builder.
Also, does anyone know where I can get some decent in-depth info on this subject I can't find much!

Inifinite Click-Through for SQL Server 2005 Report Server
Amit Diwan
In fact yes, especially if you create report in Report Builder and then only modify it in Report Designer.
If you create new report in report deisgner from scratch or adding new drillable textboxes to existing RB report you will need to copy logic in <Action> element created by Report Builder.
JasonJackson
It only works with Reports built by Report Builder.
ReportBuilder reports use semantic queries that execute against semantic models stored on Report Server. Infinite drillthru is a feature of semantic models.
http://blogs.msdn.com/bobmeyers/default.aspx
phillee
Wayne Tanner