Basic inventory includes OS name. It should populate these tables:
- AeX AC Client Agent
- AeX AC Client Connectivity
- AeX AC Discovery
- AeX AC Identification
- AeX AC Location
- AeX AC NT Services
- AeX Primary User
- AeX AC Roles
- AeX AC TCPIP
So it should be reporting. Are you using the latest NS6 release? Are the systems in question 64-bit? Is OS Name the only missing data, and all of the rest of the data (above) is reported? Even resource discovery should return OS Name, so that's odd.