NPM will monitor servers through WMI. If your needs are to monitor the server as a whole (Up/Down, CPU, Memory, Disk Space, etc) then NPM is perfect. If you need to monitor the performance and status of a specific application on your server, such as the FTP application, then you will need SAM. SAM will allow you to monitor processes, services, event log and even custom data collected by a script, pretty powerful stuff.
This is a broad answer but If you're having trouble deciding which one you really need or if you have more questions feel free to PM me and I'd be happy to help you out.
