...the whole estate is going to 64-bit Win7 from 32-bit XP, you will need to do a pretty major re-training program.and a massive purchase of new licenses, hardware etc.* That's a big shake-up!
This would be the perfect time to take a small test group and try them out on a Linux distro (perhaps use one that can be skinned to look like XP). You'll still have training to do, but hopefully less than Win7.
The savings? Potentially: licenses, hardware, downtime etc
I am not saying it's an answer that will fix all problems, but where is the harm in trying?
*I have moved from 32-bit XP to 64-bit Win7. Win7 gives me pain (mostly poor performance) every single day. For want of a few minor features, I'd go 100% Linux in a heartbeat. The missing features are: RDP - Linux does not have a decent remote desktop server, VNC sucks; and OCS - there is no client that can fully connect (audio, video etc). Everything else is equivalent to or better than Win7.