For windows 2003 cluster, check my old tutorial on following link.
Windows 2008 R2 Cluster Requirements:
1. Two Systems with Same Hardware Configuration.
2. Two Network Card
3. Windows 2008 R2 Enterprise Edition on both systems with same patch level.
4. Active Directory
5. Shared Storage( SAN or iSCSI)
6. Both servers should be the member of same domain.
7. We need a normal domain user id which will be the member of local administrators group on both servers.
1. We used Microsoft iSCSI Target on one of our Windows 2008 R2 Enterprise 64 Bit server. We had 400 GB free space on that server, so we download (following link) install Microsoft iSCSI Target.
2. We also installed Windows 2008 R2 Enterprise server on two virtual systems on VMWare ESXi Server.
3. Added Failover cluster features and enabled iSCSI Initiator on both virtual servers.
After installing we added virtual disk on MS iSCSI Target.