I'm getting a Nokia N800 soon, thought I would install the devkit. Mostly it went ok, but there were a few problems that I hope I can help others avoid...
Particularly helpful was plaes.org Gentoo archive. the key bits here were:

the specific instructions for the emerge are: 
USE="arm i386" emerge -pv scratchbox \
scratchbox-devkit-debian scratchbox-devkit-perl \
scratchbox-devkit-cputransp  scratchbox-devkit-doctools  \
scratchbox-toolchain-cs2005q3_2-glibc
to make this work add the ~x86 flag for sys-devel/scratchbox etc in /etc/portage/package.keywords
problems I ran into that are probably more related to the scratchbox install: I was concerned about the various "Run 'apt-get update' inside scratchbox to read package index files." messages. gentoo doesn't have apt-get, but turned out it is ok as this is part of the maemo install.

problem was, apt-get calls in the install scripts failed because site names wouldn't resolve. the solution was to copy my /etc/resolv.conf to /scratchbox/etc/ .

actually running the maemo scripts: (maemo install.txt)

I didn't do the maemo-scratchbox-install_3.1.sh script, assuming that the gentoo emerge had done it all.

due to the various problems above, maemo-sdk-install_3.1.sh did not complete. on some of the early errors it would restart, but eventually it thought everything was there and then said "run with -f to redownload the files", and exited. this seems to be an error in the script, if you pass it the -c option it shouldn't dump out. I commented out the 'exit 1' at this point in the script and let it carry on.

I didn't have to do the virtual packages stuff from the plaes.org page as the install script (eventually) got all the way through, thus on to section 3.3 in the install instructions.

note that once you get this far, or maybe if you don't and you're trying to figure things out, you get "inside scratchbox" with /scratchbox/login. somewhere along the way on the scripts it dies because you've not created a user account, but that's fixed by the time you get here. to change between X86 and ARM environments it is 'sb-conf select SDK_ARMEL' or 'sb-conf select SDK_X86'

the last problem was the 'fakeroot apt-get install maemo-explicit'. this worked in the X86 environment, but failed due to errors like: 
Setting up libhildon-input-method-framework-sdk2 (2.2.8-2) ...
Updating the IM modules list for GTK+-2.4.0.../usr/sbin/update-gtk-immodules: line 22: /usr/bin/gtk-query-immodules-2.0: cannot execute binary file
....
Setting up osso-addressbook (1.20070213) ...
/var/lib/dpkg/info/osso-addressbook.postinst: line 1: /usr/bin/gconftool-2: cannot execute binary file

eventually I figured out to start scratchbox, and the install completed.
hope this helps someone else save some time ....

rob at janerob dot com       8 june 2007