OK Guys. Solution for all that have Vista 64bit OS (or other 64 bit microshit) and cant flash n900 and posible many other devices.
You need to turn on loading of unsigned drivers.
You do it by choosing option in text boot menu (the one that you will get after pushing "F8" key just on start of Windows booting).
You need to choose from text menu "Boot without checking for signed drivers" or similar (cant exactly write option name because got polish edition of Vista)
If someone can check how its called in english version properly then please write it.

Good luck.
Have a nice day.
And pray for fast firmware update (Bricked 2 times in 1 week).