I am giving you full instruction, Which will not need mmc:

1. Install root (apps manager )
2.Install leafpad (apps manager)
3.Download gingerbread for your n900 (google)

Plz don't do any mess with x-terminal

Now,
Open x-terminal
type: root
apt-get update
apt-get install nitdroid-installer
then it ask to type "Yes"
Open new x-terminal
type root
cd /home/user/MyDocs/
bzip2 -d gingerbread.tar.bz2 (wait for some time)
cd /
mkdir /and
cd /
mount /home /and
cd /and
tar xvf /home/user/MyDocs/gingerbread.tar
dpkg -i /home/user/MyDocs/NITDroid-kernel-Mido.Fayad.deb (you have to download this file)
open new x-termnal
leafpad /etc/multiboot.d/1 (then press tab on your screen)

The its done
don't forget to press thamks button