This was a major PITA to figure out, but doing it is pretty easy.
1. Download the
LG Mobile Support Tool to your Windows computer from LG
right here.
2. Install it, and while the phone is
DISCONNECTED open the program.
3. Under the Options & Help menu, choose Country & Language. Set Singapore as your country, and English as your language (unless you prefer another of the listed languages. Hillbilly was not listed.)
4. Next, on the main window choose to install the USB driver, and choose LGP500 as the model number.
5. Wait while the app downloads and installs 4 or 5 separate drivers.
6. On your Optimus One, enable USB debugging and plug it in.
You now have the ADB driver, and the USB modem drivers installed. You know what to do next.