I have successfully decompressed and mounted the rootfs.lzo. Here is the script to uncompress it. This gives you a regular ext4 image. Should work with the other lzo images, but this is not tested.

Also you need python-lzo installed. It isn't packaged for Ubuntu, but the required liblzo2-2 is in the standard repos.

http://al.robotfuzz.com/~al/maemo/unlzo