First up, you need the Debian installer from the Boxee website. If you don't already have it go ahead and download it then place it in your home directory. I'm using the AMD64 package, which is called boxee-0.9.22.13692.x86_64.modfied.deb
Login to a console, we will be working only in our home directory.
Run these commands;
dpkg-deb -x boxee-0.9.22.13692.x86_64.modfied.deb boxee
dpkg-deb --control boxee-0.9.22.13692.x86_64.modfied.deb boxee/DEBIAN
Now we need to edit the file that lists the dependencies;
Find libxmlrpc-c3 in this file and append -0 (that's a zero) to the end of it so that it now says "libxmlrpc-c3-0".
That's the only change we need to make but we do need to create a new Debian package file now that we have fixed the dependency problem.
dpkg -b boxee boxee-0.9.22.13692.x86_64.natty.deb
Before we can install Boxee, we will need to manually install all the dependencies;
sudo apt-get install libcurl3 libsdl-image1.2 libsdl-gfx1.2-4 liblzo2-2 \
libdirectfb-1.2-9 libnss3-1d flashplugin-nonfree libhal-storage1 screen \
msttcorefonts libtre5 libmad0 libxmlrpc-c3-0 libnspr4-0d xsel libmms0 libenca0
With our dependencies installed we can now install our modified package;
sudo dpkg -i boxee-0.9.22.13692.x86_64.natty.deb
And with that you should have a working Boxee on your Ubuntu Natty system.
It would be nice if the Boxee guys would update their packages occasionally but I guess the reality is that they want to make you purchase a "Boxee Box" instead.
This is the trouble with being at the mercy of the source code owner I guess. If Boxee were open source somebody would have already rebuilt the packages and we wouldn't have to dick around like this in the first place.
Update: I don't know if this is Natty specific bug, but I ran into another problem where Boxee would play video in black and white. If that happens to you, here is how to fix it.