The simple answer is SP1...
My recommendation if you are building a new cluster is that you Slipstream the service pack. It will solve a lot of issues during the install, a lot of which I had. After we slipstreamed sp1 the install went through without a hitch, except SSRS didn't install on the 2nd node! Some thing I'm still trying to get resolved. There is no way to add SSRS to the 2nd node once the build is finished without adding a new named instance.
Have a look at the Slipstream instructions here: http://support.microsoft.com/kb/955392
Leo
Senior DBA Consultant
SQL Services
Leo
Nothing in life is ever so complicated that with a little work it can't be made more complicated.