installation is really simple if you have the previous version running..although i installed via ubuntu so..it was easier for me..format your existing ext3 partition..copy rootfs onto the partition.
Then on the phone on xterm first type sudo gainroot
then mkdir /and
then mount /dev/mmcbkl1p2 /and
then simply run dpkg -i /home/user/MyDocs/.nitroid/nitdroid-ke(press tab it will auto complete the filename)
and press enter.
Reboot select your ooption on multi boot