I just got back from an on-site assignment in Denver. W were migrating to SQL 2008 on a new set of Windows 2008 clustered servers and ran into an installer bug. We completed the install of the first node but the install failed for the second node because of an invalid product SKU. The SKU was valid. It was slipstreamed in by Microsoft when the product was purchased and downloaded. It appeared correctly in the SKU input box just before the error. We tried several times with the same result and eventually called Microsoft.
Microsoft is well aware of the bug and has a hotfix which, unfortunately, didn't work for us either. Microsoft and others have also posted workarounds which all involve running setup from the command prompt with a varying number of parameters, depending on who you are talking to. Microsoft's example has an enormous number of parameters which you can find by following links from these pages: https://connect.microsoft.com/SQLServer/feedback/ViewFeedback.aspx?FeedbackID=363036
What finally worked for us was very simple: Execute this in the command prompt while logged in as an admin:
setup.exe /ACTION=AddNode /INSTANCENAME="MSSQLSERVER"
By the way, the install process for clustered instances has changed significantly. Now the cluster wizard has been broken into two wizards, one creates a single-node cluster (whatever that means). Then you must go back to the setup start screen and run the Add Node wizard for each node you want to add. You must run it from the node you want to add, not the primary node. SQL Server binaries are not moved to the second node until you do that.