I hate to sound like such a n00b.
I'm giving up on this. I have a folder on the 2nd PC which is shared with the first (this) one but can't access it. The folder in question here isn't seen on the 2nd machine so apparently it is not shared.
My explorer window shows both Home Group and Network.
Computer type PC/Desktop System Manufacturer/Model Number Home Built Desktop By DataTech OS Windows 7 Ultimate X64 SP1 CPU Intel i5-2550K, Differing ~4.4-4.8GHz No built in GPU Motherboard ASUS P8Z68-V PRO/GEN3 Memory 16GB G.Skill Sniper 2133MHz 4x4GB Graphics Card ASUS ENGTX460 DirectCU/2DI/1GD5 GeForce GTX 460 Sound Card Onboard Realtek 5-1 Monitor(s) Displays Samsung P2570HD Screen Resolution 1920x1080
Keyboard Old, beat-up Dell USB From 10 yrs Ago Mouse Gigabyte m6900 wired PSU Corsair HX650W Case Inwin Dragon Rider Cooling Hyper 212 EVO w/two Noctua fans, push-pull, @1300 RPM Hard Drives Crucial M4 128GB for OS, 750GB Seagate MomentusXT for data, 500GB Seagate Constellation for storage Internet Speed 8-19 Mbs down, 3-4 Mbs up Comcast Cable Antivirus Norton Internet Security Browser IE 9, Opera when needed Other Info 4 case fans, LG BluRay-RE, ASUS DVD-RW, Mr. Fusion power generator with flux capacitor, 1.21 gigawatts.