1)     Connect your phone to the pc.
2)    Click on Mass storage mode
3)    On your pc Place the n900es.avi file to the root of your n900. (the root is the main folder)
4)    Disconnect your phone from the pc & Open X Terminal on your phone.
5)    Type the following commands CASE SENSITIVE: sudo gainroot
6)    cd MyDocs
7)    ls (now should see in the list the n900es.avi file)
mv n900es.avi /usr/share/hildon-welcome/media/
9)    cd /usr/share/hildon-welcome/media/
10)  mv Hands-v32-h264.avi Hands-v32-h264.avi.bkup
11)   mv n900es.avi Hands-v32-h264.avi