This isn't looking good. From a Linux system, I first tried simply resetting the device using flasher:

"./flasher -R"

That didn't work, so I tried actually flashing it:

"./flasher -F Nokia_770_SE2005_3_2005_51-13.bin -f -R"

In both cases, I never got past "Suitable USB device not found, waiting". However, I could hear the Linux system's disk churning a little about once a second when I was holding the 770's power button, making me think my Linux system is seeing the same USB plug-unplug cycling I got on my WinXP system.

This is the first time I've tried to flash my 770, although the whole saga began when I took out the battery to get the product ID so I could flash-up to the latest release. I know positively the 770 + USB cable + WinXP system combination worked before, because I'd used it to move files on and off the MMC.