Native installation is based on kexec. Default Maemo kernel however doesn't have support for it so it needs to be replaced first.
You can either install the "kernel-power-flasher" package from Maemo extras section System (this kernel package is NOT provided by Nokia, so use is at your own risk) or you can compile and install a fremantle kernel with following patches yourself.
There is currently a bug related to the DSS2 driver which causes a flood of messages to the screen on a kexec'ed 2.6.33 kernel. Otherwise, things work.
Instructions for compiling Maemo kernel can be found from: Maemo kernel guide
Create a symbolic link on N900 so that existing kernel modules will be used with the new kernel.
cd /lib/modules ln -s 2.6.28-omap1 2.6.28-omap1-kexec-patched
Flash the patched kernel:
flasher -f -k zImage-kexec-patched
Install kexec-tools user space application from Maemo-extras repository.
Install Meego image on external micro mmc card.
sudo moblin-image-writer <image-file>
Connect external micro mmc card.
kexec -l /boot/zImage-2.6.33 --command-line="init=/sbin/init rootwait root=/dev/mmcblk0p1 rw console=ttyS2,115200n8" sync kexec -e