On systems that are set to auto-negotiate speed and duplex is there is there a command line query or status window that will tell me whether full or half is in use?

Not in Windows. Some NIC vendors provide a 3rd party application that you can run to further manage and view stats on the Network interface cards, including speed and duplex settings. Visit: anITKB.com, an IT Knowledge Base.

Really? Seems like basic info. Every driver needs to know what mode it's in and every switch knows what mode each channel is in. Maybe there's no particular reason that Windows above the driver needs to know but I'm dumbfounded there isn't some way to query the driver, other than apparently get a collection of 3rd party tools depending on the NIC.

A suggestion from another user was to check the event log. I did on several systems. Most will report an event about connection established at some rate and duplex, so that helps. One Intel NIC didn't give any such message.

If you are using Intel NICs, you can get driver/software package which includes the proSet package. Visit: anITKB.com, an IT Knowledge Base.