I flashed my N900 several times in the last couple of days from Ubuntu. Basically, I start the flashing program and wait till I get the message aboutthe suitable USB not found, then I grab the USB cable and plug it and the N900 in and it starts flashing.

Interestingly, I found that after flashing the Emmc I had to reboot the N900 to continue flashing. I know, the wiki says NEVER to reboot between flashes like that. The Wiki can't always be trusted.