Is there a Windows Virtual Machine for the iPad?
If so, has anyone used it, and how was the performance?
I would really recommend Onlive desktop for iPad. It is totally FREE and it comes with microsoft office. It also has a cloud feature that lets you access your files on your computer
Not possible. However, you can host a VM on a separate desktop or in the cloud and access that from your iPad; vmware or parallels both now offer this. Stay away from VNC type solutions though; far too slow.
I disagree that VNC type solutions are too slow, as it depends a lot on the server hardware and the network connectivity. I have given Citrix, Go-Global and even vanilla RDP solutions to enterprise customers, where they even run home grown heavy client server architecture based ERPs with these solution on iPAD/Android tablets and really not faced too much of lag issue. We need to do proper server sizing and network planning as once the connection is established, the tablets acts like dump terminals (aka likewise to yesteryears unix terminals).
I'm not aware of any stand-alone virtualization on the iPad.
All of them require a virtual environment being installed on a remote hardware or offered via the cloud. The Apps then grant access to this environment similar to either VNC or Terminal Services. Performance relies on the host hardware and experience depends on your connection type and speed.
VMware brings virtual machines to iPad
Yes there are quite a few. You can run windows in a VM mode as you propose, but I find it better to connect via a RDP client to the Windows Server running terminal service. VMWare, Citrix, Ericom, 2X, Wyse, Parallel Desktop, Go-Global, etc. lots of solution available.
I will highly suggest you to install the free client Ericom AccessToGo Remote Desktop/RDP Client because they have already two demo connections setup in the software. One is through normal RDP and another is through their proprietary Fast RDP. They already have a Windows server configured with them so you can just tap these demo connection, connect to their server, invoke the windows environment and check out the windows performance in reality. I think that will be a real hands on for you to check if the solution will be feasible or not.
Also go through this url for details to your question asked : http://www.lostintechnology.com/windows/how-to-run-windows-on-ipad/
Also found a related great resource for you, certainly check it out : http://www2.bus.umich.edu/MyiMpact/technology/ipad-virtual-lab-installation