Okay, since I just got a brand new laptop, I did a fresh install of Windows 7 SP1 on it, and plugged in my S3 with the Samsung-supplied USB cable.
Got the USB confirmation beeps, and Windows attempted to install drivers, with this result:
USB Composite Device -- Ready to use
CDC Serial -- No driver found
SCH-I535 -- Ready to use
SAMSUNG_Android-SCHI535 -- No driver found
S3 didn't show up as a drive.
Unplugged S3 and installed the drivers linked to by
darkestred above (irritatingly, the package also tries to install three items of bloatware, making me wonder if they're really from Samsung).
Plugged S3 in again, and got this result:
USB Composite Device -- Ready to use
CDC Serial -- Ready to use
SCH-I535 -- Ready to use
SAMSUNG_Android-SCHI535 -- Finished; restart required
S3 didn't show up as a drive, so rebooted the laptop. Plugged the S3 back in...USB noises from both laptop and phone...but still no drives showing up.
I checked Device Manager with the S3 plugged in: No errors shown. The following entries were found:
Portable Devices
SCH-I535
SAMSUNG Android Phone
SAMSUNG Android ADB Interface
Universal Serial Bus controllers
SAMSUNG Mobile USB Composite Device
Turning my attention to the S3, the Notification Bar shows that it's connected as a Media Device (MTP). USB debugging is checked, but the above connections are unchanged even with USB debugging unchecked.
And still doesn't show up as a drive...or drives, since I have also have a 32 GB card plugged into the S3.
Sigh.