I can't see any problem with install Open Office for your department to use, as has been already said it like any other piece of software. From what you have said your NM seems to be saying he would not install any Open Source software at all! There is a lot of OS software out there, which the LEAs will tell the schools to install, for example Audacity is used by most music departments with the blessing of the LEAs advisors..
I have installed both MS Office & Open Office together on a number of schools network will out any problem. Open Office is easier then most education software to install on a network anyway.
I had one special school I had the same request from 2 members of staff who want to use open office this is going back about 4 /5 years ago and the school was still running NT Server, so I downloaded the portable open office installed it onto a network share and put the icon on the staff desktop, about 5 min work. All the files are installed into that one directory & the program runs from there without install any files on the clients.
Ok not that fasted to open but for only 2 users fine!! Also easy to upgrade as only one set of files to do!! Now will Windows 2003 I would just use an msi to install it over the whole network.
I would asked your NM to do the portable open office to a network share, or a portable open office install to a directory on each PC in your department, that way no files are install into the reg or windows system folders on any of the PCs and any problem you just delete the directory and its gone.
Hope this help..
Ste