I spent a little time over the last few days getting Debian linux installed and running on my N810. This install did not replace the Maemo linux that was already on the 810 but runs on top of it in a chroot.
Read here what to do:
Its hard to believe this is running on a PDA! Here are a few screenshots of LXDE running on top of Maemo. Many thanks to qole over at InternetTabletTalk.com for putting this together for those of us that dont want to take the time to do this the hard way