ica, you are not making something wrong. Only Windows is kicking your a**.

The last thing missing is a driver (inf file) for the N900 usb mode.
This inf file is created by inf-wizard.exe which is contained in libusb-win32.zip in the /bin folder.

Extract the zip to any folder, start inf-wizard.exe as Administrator and follow this instructions.

You may still run into problems installing the inf/driver because it is unsigned.
Maybe it is just hitting "install anyway" when asked.

EDIT: Peter got a perfect explanation link above while i am typing


And do not scare away from the instructions for halftux image if you decide windows has had enough tries.

In simple words, live image boot explained.

1. Download this image containing all the stuff.
2. Download and install Win32DiskImager
3. Open Win32DiskImager and select the iso image you downloaded to be copied to an empty usb-stick.
4. Boot your computer from the USB-stick.

Do not worry, nothing will be changed or even damaged in your windows as it will not be touched.
If your computer does not boot from the usb stick when your leave it in during reboot, you may have to enter your computers bios by hitting a key during the first 5 seconds after power on.
Usually it is DEL or F2 or ENTER. Once in the BIOS, look for startup/boot options and set the usb device higher in boot priority by moving it up in the list of boot devices. Generally this is done with F5(up) and F6 (down).

If all is set to boot from USB, you will see a debian command prompt after boot up has finished.
It is an actual linux running from USB drive.

From there on i would explain further if you got there.