mmcblk0p2 is the name of device. In this case, it's flash memory 0 and partition 2. If it's 0 then it means that you are changing the _main_ memory of the phone. To work with sd-card, it has to be 1.
ex. mmcblk1p2 sd-card; partition 2
To install new android, you need simply extract it to the partition where it's installed.

Keep in mind that flash memory numbers are in reverse when phone is in multiboot.

Steps:

sudo gainroot
mount /dev/mmcblk1p2 /and #partition 2 on the flash card
rm -rf /and/* #delete old android files
cd /tmp
wget http://downloads.nitdroid.com/e-yes/...-0.0.9.tar.bz2
tar -xvjf NITDroid-0.0.9.tar.bz2 -C /and


Should work, but there is a chance that I made a mistake and something will go wrong, so make a backup.
Also, there is newer android (2.3). If you want to install it, just change NITDROID-0.0.9.. to
gingerbread