Changing page permissions on virtual address

I was wondering the best way to change page permissions on a virtual
address for nt4. (for exampe to go from read to write)

In windows 2k/xp/2003 you can you ZwProtectVirtualMemory, however on nt4
you cannot (at least not that I am aware of). So my questions are as
follows a) is there any documented way to do this and if not b) how can
one do this reliably in a driver - there must be a way.

Thanks.