Your IT department isn't necessarily being over zealous. I have to support more than 5000 desktop and laptop units in my geographic location alone and my company supports more than 40,000 company wide. We JUST migrated to Windows 7. Maintaining a consistent OS installation footprint is very important to ensure security on your company network, and reduce the amount of support needed to keep things running smoothly. Cut your IT guys a little slack here.
Having said all of that, we do have some Windows 8 units in our environment that are very segregated for testing purposes, but I foresee our next migration being to Windows 9 (not 8) based on past experience.
To the gentlemen suggesting running Windows 7 on a virtual machine, this could cause a switch security alert depending upon the sophistication of the network, and severity of security protocols implemented on the switch. Some organizations will disable a port as soon as is sees a second MAC address accessing the port (which the VM will create).
Append: On the subject of installing Windows 7 in general practice, I'd certainly be interested in hearing how that goes. I suspect (as mentioned by someone else) that you will run into severe trouble on the driver front, but It'd be interesting to see if you could do it.
