Advantages of Win 2008 cluster over Win 2003 cluster

Team,
I have to upgrade SQL Server 2005 EE 64bit Active/Active cluster on Windows 2003 to SQL Server 2008 EE 64bit
Is it recommended to upgrade the OS also?
1. If so, What are the benefits we have on Windows 2008 OS over 2003 especially on clustering side
2. I prefer to do side by side upgrade. Since there is limitation on hardware resources, can we use scaled down version of hardware
similar to Production and once installation and testing is successfull, shift the resources (CPU and Memory) from production to new instance?
Regards
Prabhu S

The benefits are the enhancing performance and simplicity of installation , either for windows 2008 clustering or sql 2008 clustering.

check: http://technet.microsoft.com/en-us/library/cc770625.aspx

on the other side , not all cluster hardware are supported by windows 2008 , you should carefully review and check hardware compatability level with your vendor

Parallel SCSI support in Windows Server 2008 Failover Clusters has been removed. It should be replaced with SAS solutions.
Windows Server 2008 Failover Clusters support only the following types of storage connections:
SAS , iSCSI (not scsci), Fibre Channel
you should need extra cost for licence upgrade for windows 2008 , sql 2008
Except you have your reasons for that upgrade, you must build technical and financial plan against benefits you gain.

well thanks a lot for your informaition