Nick MacKechnie posted a great post about Hyper-V maximum supported configurations.

Topics:

• Operating System Requirements
• Hardware Requirements
• Virtual Machine Architecture Support
• Memory
• Processors
• Networking
• Physical Storage
• Virtual Hard Disks
• Virtual Storage Controllers
• Virtual Storage
• Virtual CD/DVD
• Virtual Serial (COM) Ports
• Virtual Floppy Drive
• Number of Virtual Machines

Read the complete post at http://exchange.si/archive/2008/07/10/hyper-v-maximum-supported-configurations.aspx