Well I am doing more work on this today to see if I can get a solution for my Windows 7 users (including myself). And it turns out that print driver isolation is exclusively a feature of Windows Server 2008 R2 only. And I have only one R2 server in the whole school, which is also our Remote Desktop and RD Gateway server. So I will have to try out some print queues on that, less than ideal so I will have to get another R2 license eventually.
The interesting thing was that after I had installed the printer on the RD server and isolated its drivers, it is using WinPrint instead of BrPrint. When I installed another HL5140 onto a standard 2008 server it is still using BrPrint. So the isolation system must force the WinPrint processor to be used.
Another possible workaround, which I am also going to test, is to change the existing print queues to use WinPrint instead of BrPrint. I guess the root problem is that Brother has not updated BrPrint to be compatible with Windows 7. The drivers provided are for Windows Vista or 2008 at the latest. It may turn out there is a compatibility issue with BrPrint on Windows 7 and this is not going to be fixed by Brother because this printer is too old. At this stage I don’t have any experience of what happens when you change print processors so we will try out both options side by side to see.