Hi, guys, I'm not a technical staff, but found a very nice way to free much more space on root. The original link is http://www.maemoers.com/thread-162-1-1.html. It was quite easy, just several command lines in your x-termal (just copy & paste the following commands into your x-termal,

1) root
2) rm -r /home/root/
3) root
4)
mkdir -p /home/root/usr/share
cd /usr/
for FILE in games include local src var
do
mv $FILE /home/root/usr/
ln -s /home/root/usr/$FILE /usr/
done

mkdir -p /home/root/var/cache
cd /var/cache/
for FILE in apt
do
mv $FILE /home/root/var/cache/
ln -s /home/root/var/cache/$FILE /var/cache/
done

cd /usr/share/
for FILE in fonts icons locale mime nokia-maps pixmaps sounds themes tutorial-applet zoneinfo
do
mv $FILE /home/root/usr/share/
ln -s /home/root/usr/share/$FILE /usr/share/
done

mkdir /home/root/usr/share/games
ln -s /home/root/usr/share/games

I did this, and found free space on my root jumped to 93mb from 60mb before. Everything works normal.

NOTE: just do this one time, since when i did it second time, my n900 firewire was broken. I have to reflash it myself. So, please do backup your files before doing this, and it might be risky although it works fine for me.