I was given a virtual (.vhd) made using Hyper-V (it's a windows server 2008). I am running windows 7 enterprise on my box. Which client should I download for best performance.
No client necessary to see what's in there. Open Computer Management (Start -> Right click Computer -> Manage). Find Disk Management. Right click it, attach VHD; select the file and it will appear as a new HD in the computer.
On the off chance that you're trying to run the VM that's on the VHD, there's only one Virtual PC for Windows 7, there are no choices (the other versions don't run on 7). Note, Virtual PC is 32-bit only; if the VM is 64-bit it will not run on Windows 7.