Quick post, was building a SQL 2008 Active / Passive cluster today on Windows 2003 x64 and got stuck when adding the second node.
Turns out to be a bug in the install media. Microsoft has a hotfix posted but that doesn’t seem to work correctly.
Got the correct fix from here:
In the install media folder under \x64 find the DefaultSetup.ini file.
Just comment out the key (while you’re in the file copy the key) and put the key in during the installation.