Using Windows XP SP3 here...

I fixed the problem by updating the driver through device manager. The N900 showed up on device manager with a yellow exclamation mark on it, so I right clicked on it and picked "update driver". It went on the internet and grabbed whatever update was there and my PC then recognized the N900.

On device manger it created a new device type called Wireless Communication Devices and under that it listed Nokia BB5 ADL Loader USB Generic and Nokia BB5 ADL Loader USB Phone Parent

My dos window then showed that it had recognized the device and started the flash process.

Suitable USB device not found, waiting.
USB device found found at bus bus-0, device address \\.\libusb0-0001--0x0421-0x0
105.
Found device RX-51, hardware revision 2204
NOLO version 1.4.14
Version of 'sw-release': RX-51_2009SE_10.2010.19-1_PR_MR0
Sending xloader image (14 kB)...
100% (14 of 0 kB, avg. 14 kB/s)
Sending secondary image (106 kB)...
100% (106 of 0 kB, avg. 106 kB/s)
Flashing bootloader... done.
Sending cmt-2nd image (79 kB)...
100% (79 of 0 kB, avg. 79 kB/s)
Sending cmt-algo image (507 kB)...
100% (507 of 0 kB, avg. 507 kB/s)
Sending cmt-mcusw image (5826 kB)...
100% (5826 of 0 kB, avg. 5826 kB/s)
Flashing cmt-mcusw... done.
Sending kernel image (1705 kB)...
100% (1705 of 0 kB, avg. 1705 kB/s)
Flashing kernel... done.
Sending and flashing rootfs image (185728 kB)...
100% (185728 of 0 kB, avg. 185728 kB/s)
Finishing flashing... done
CMT flashed successfully

Note my N900 didn't reboot after the flashing was complete as some tutorials have stated...so i waited a bit and still no reboot. In the end I had to manually turn it on.

It also took a minute or two to reboot which seemed like an eternity and I was getting quite worried. The row of dots appeared on the screen and nothing much happened for a minute or two.

Finally it did boot *phew* and I got the screen to set the region and time zone.

I noticed that flashing the device did not erase any of my data like my pictures, sound files, videos, phone contacts, sms conversations, web browsing history, etc - which I was hoping it might do. I wanted the device to be exactly what I first got from the store, but this wasn't the case because all my data is still there.

Hope that helps.