There are a few guides on this already (especially the Windows part), but I figured I’d write something anyhow. I’ve recently come into a small set of Windows servers that need to be added to my Observium installation. The SNMP setup is easy, but it lacks good reporting for CPU, RAM, and MSSQL metrics.
Observium has a WMI Poller module, which requires getting the “wmic” utility running on Linux. I poked around a lot at this, and found a simple short process which is notated below. Hopefully it helps! This was tested on Debian 8 “Jessie” and Ubuntu 14.04 LTS.