Hi Peter and sgivoni,
yes you are right, the answer is not accurate and I apologise for that.
The correct answer should have been, as you said, in Reporting Services Project in BIDS.
Today I checked in the Feb CTP version of SQL Server 2008 and it's not there either.
In SSMS we can browse the cube but there is no facility to view the MDX.
Ditto for the "Browse Cube" tab in the Analysis Services Project in BIDS.
The only place in SQL Server 2008 where we can browse the cube and view the MDX is in the Query Designer of a Reporting Services Project.
Personally, in the current project I use ProClarity to browse a cube or view the MDX, rather than using using BIDS or SSMS. I found that the cube browser more user friendly. But to compose/type queries manually I use SSMS.