Even though our title says Developer, it's hard for most of us to escape doing a system administrator task once in a while.
I had to add SQL Server Reporting Services to an existing SQL Server 2005 installation. This shouldn't be a big deal. Mount the SQL Server installation image, run the setup and follow the installation wizard to add extra components. Arriving at the step where I should be able to select Reporting Services, the Reporting Services option was grayed out.
After some Googling I found out that IIS needs to be installed to be able to install Reporting Services. I opened the Services snap-in and saw that the World Wide Web Publishing service already was installed, but it wasn't running... After starting the service, the Reporting Services option was no longer grayed out. The installer should have been smart enough to give a hint in my opinion, terrible user experience.
So to make a long story short, make sure IIS is installed and that the World Web Web Publishing service is running!
I hope I was able to soften some of the system administrator pain.