You can monitor your network with Zenoss Core on the VMware image with VMware Player on Windows. It's open source (and free), and it can monitor your switches, routers, Linux/Unix and Windows servers natively and just about everything else on your network. You'll get availability and performance monitoring, as well as modeling your network and devices with the integrated CMDB. Plus it's all remote-monitoring (no agents) and there's a large and active community of users. I'm a bit biased, but it sounds like it does everything you'll need.
Thanks,
Matt Ray
Zenoss Community Manager
[email protected]