I confirm my method works:

HOW TO MAKE NOKIA MAP LOADER WORK IN WIN 7 64-BIT
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1) Find the .qf file in the root dir of the n900 phone's flash memory

2) Make a copy of the .qf file, and rename it to "qf" (without the dot in front, unhides the file) in the root dir of the n900 phone's flash memory

3) Make another same copy of the file named "qf" and put it into the root dir of the sd card as well

4) Use the n900 in PC Suite Mode with Nokia Map Loader

Notes:
So there are 2 identical files named "qf", one on sd card and one in phone memory. The 2 qf files seem to appear as 1 file in PC Suite mode, and the n900 is detected in PC Suite mode.

Nokia Map Loader seems to report the capacity of the sd card, but the maps are actually loaded to the phone's flash memory. I'm not sure what happens when you exceed that limit or try something funny.

I'm interested in any comments whether this method works with Windows Vista 32/64-bit and Windows 7 32-bit.

P.S. I'm using Win 7 64-bit, Nokia Map Loader version 3.0.28.0.

P.P.S. Virtual PC eats resources and is a hassle, that is why I try to avoid XP Mode.