Here is the procedure to flash the n900 using maemo flasher-3.5.
downlaod meamo flasher-3.5 just type it in google you will find it.
First go to http://tablets-dev.nokia.com/nokia_N900.php and download
Two files : (1) RX-51_2009SE_20.2010.36-2.004_PR_COMBINED_004_ARM.bin (for flashing)
(2) and if you want to format your emmc then download RX-51_2009SE_10.2010.13-2.VANILLA_PR_EMMC_MR0_ARM.bin
The now open meamo flasher-3.5,switch off your mobile and hold u button and plug in the usb your n900 will show you logo of nokia with a usb connected signal

If you want to format your emmc also then type : flasher_3.5.exe -F RX-51_2009SE_10.2010.13-2.VANILLA_PR_EMMC_MR0_ARM.bin -f -R

OR if you want to flash fw then:

flasher-3.5.exe -F RX-51_2009SE_20.2010.36-2.004_PR_COMBINED_004_ARM.bin -f -R