SNMP on Win2003 - Perfmib files missing

Hello,

I have a number of Windows 2003 servers missong OID's for processor
load and memory usage, among others. It's not consistent among
servers. It seems to be on systems that are missing the Perfmib files
(perfmib.mib, perfmib.ini, perfmib.dll), so it makes a certain amount
of sense. However, it's not clear to me, nor am I able to Google any
info on, why perfmib.mib isn't present or how to add it. Obviously I
can copy the files over, but that does nothing.
Can anyone clue me in as to how to rectify this?

Thanks!
Toni