You have 2 options:
- If you want to collect packets form a switch spanned port, you'll need to deploy a Network Sensor (NPAS) on a Windows machine and feed it with the duplicated packets from the span.
- If you want to collect packets that go in and out an application, you'll need to deploy a Server Sensor (SPAS) on the windows machine that supports this application. No need for a switch spanned port.
You usually don't have to do both.
The result might ultimately be similar, but the first one is easier for network guys and the second one for server guys
More here: http://www.solarwinds.com/documentation/Orion/docs/SolarWindsPacketAnalysisSensorDeploymentGuide.pdf