I have rebooted and the USB drive is still unrecognized. However, the USB device error message went away. How? I reconfigured the Generic USB Drive in Device Manager for "configured for performance," meaning that it must be 'safely removed' before I can free the port. When it initially was recognized by Vista, it was as a Plug and Play, and this classification seems to have been the only thing prompting the exclamation point next to the Generic USB Device in Device Manager. So that error's gone.
But it still won't open.
The HDD enclosure came with a disk with drivers. However, Vista doesn't recognize any of them in a Device Install, and also the instructions are written by Chinese people (yes, I mean literally: the CD's name is "我的光碟", which is probably Mandarin for "HA YOU'RE A CHUMP").
Instructions on the disk about possible problems:
1. Make sure the USB cable is properly connected to your computer.
2. Make sure the power supply provides enough power.
3. For Windows 98 the driver is installation.
4. Some hard disk must be set to master mode.
5. Delete the “USB Mass Storage Device” from the “USB Controller”
I'm going to try Number Five now because I have no idea how to do Number Four. Of course, I'm going to restart.