Sflow on Windows Server

have you had a look at nProbe ?

Here is a Thwack Product Blog post that talks explicitly about deploying nProbe used in conjunction with Orion NTA. This allows for you to analyze bandwidth hogs without flow capable network equipment

Is nProbe the only option apart from the protocol being enabled directly on the device?  Or are there others ?

nProbe will enable the protocol on a Unix, Mac, Solaris or Windows machine/server.

When you talk about "device", are you referring to a server or a network attached device? If you are talking about a non-netflow enabled device, you could mirror a switch port and analyze the traffic with a converter (ie fprobe or NDSAD  as found here: NetFlow Tools)

Also, keep in mind that NTM analyze other type of metrics, like Cisco NetFlow, Juniper J-Flow, IPFIX, sFlow, Huawei NetStream & other flow data

Sorry, yes, I was thinking "device" as in a switch, not a server.  Our Adtran 1544 L3 switches are not netflow-capable.  We have a "Network Agent" from Websense, installed on a physical server that is connected to a mirrored port on one of the 1544's for our web filtering.  We have NTA, and have started looking into using nProbe, but I'm wondering if I can install it on the same server as the Network Agent, (since they are doing similar things), or if I need even another server to monitor another mirrored port. And is it possible to even mirror a port twice?  (to two separate ports)

If you consider this question closed, please mark it as answered. If not, do not hesitate to elaborate so we can help you better

Regards!