For v9.0, the discovery portion picks up the device type via snmp only... so you've probably not done anything incorrect. In this instance, I would assume the snmp agent isn't on. As for the 2950, I'm not entirely sure why it would show up as unknown.
The good news is that you can edit the properties of a device and change the device type to what you want. From the device tab, drill down into a device until you're looking at its monitors, then click ... edit > properties. Next, toggle the "Property Refresh Policy" and change whatever you like!
For the 2950, to troubleshoot, can you try going to the Devices tab and selecting Add > New Device and attempting to add it again? It should give you the option to leverage previously discovered monitors or rescan. Try rescanning to see if the interface monitors show up. You can go back and enter other community strings to see if that makes any difference. You might also see if there are any firewall settings that would prohibit SNMP requests from getting to your device.