I was stuck with the same problem. I thought I had bricked my N900 when I was unable to flash the EMMC. Rootfs flashed just fine. I tried flashing through Windows 7 (64 bit), Windows XP 32-bit, and even Windows 2000 through vmware. All of them hung on "Suitable USB device not found.."

I hadn't tried Linux because I was determined to get it working through Windows and I had heard others doing it before. But the results were so inconsistent, I caved in and tried Linux.

I boot into Ubuntu, went through the same process, and it worked on the first try. The USB device was found immediately.