OK, so I uninstalled KIES and the drivers.
I then tried to install the drivers. No go: The installer continues to fail, with the progress bar at around 80-90%. I experimented with running the installer as administrator, installing off of \Program Files (x86) and off of \SAMSUNG, instead of the default \Program Files, and still no go.
I then re-installed KIES, turned off debug in the phone, and plugged it in. Win7 installed a driver for the phone and all was well.
I then unplugged the phone, turned on debug, and plugged it back it. Now Win7 installed the following drivers:
USB Composite Device
USB Mass Storage Device
Android UMS Composite USB Device (two of these!)
and said they're ready to use. But it also tried to install:
and it gave "Driver not found" for these.
And "adb devices" lists nothing.
To make sure adb works fine I then plugged in a Kindle Fire. Windows set up the drivers for it and it showed up in "adb devices" just fine.