Warning: By following these instruction you might cause damage to your N900 device. Make sure that you create a backup of your device before continuing. We do not take any responsibility of the damage that might be caused to your device.
Some additional package are required to be installed to your Fremantle installation in order to get the dual boot working. This includes kexec-tools, kernel with kexec support and bootmenu.
apt-get install kexec-tools
In order to boot MeeGo from your Fremantle installation you need to install kernel that supports kexec, that can be found from HERE.
If you wish to have bootmenu to select either Fremantle or MeeGo during boot you need to install bootmenu to your device. The bootmenu can be installed from HERE.
Next we install MeeGo to external micro SD card (size >= 2G). NOTE: The content of the card will be deleted, so copy all essential data to safe location before continuing.
The image can be written with ...
You can boot to MeeGo with bootmenu (if installed) or with kexec command.