SSC Serv now has a Librato plug-in that allows you to send Windows system and performance metrics directly to your Librato account.
If you search collectd.org for a Windows client they will point you to SSC Serv. SSC Serv is similar to collectd in that it uses the collectd network protocol and tracks the same type of system metrics. The full version requires a license but they also provide a free version that is limited to the CPU and Interface plug-ins.
Setup is simple. Generate a "record-only" API token, enter your account email and you're done.
To learn more about SSC Serv visit http://ssc-serv.com/.