AIMehdi:

1. Install Easy Debian on your N900.
2. Download and decompress this Ubuntu image: ubuntu-m5-v1.img.ext2.lzma
3. Edit /home/user/.chroot to point to the Ubuntu image
4. Use the "Debian chroot" icon to get to an Ubuntu root terminal.
5. apt-get install the necessary packages to run Gnome
6. modify the xephwm5 script to start Gnome on DISPLAY :1 instead of LXDE (but why Gnome? )

You might also need the /bin/qobi-wmhint-fix binary from the current Easy Debian image, or you can get it from this post. This fixes keyboard problems better...