Hi, welcome to the forums,
It should run on an N800, but you'd need to grab my old packages from here :
http://kakaroto.homelinux.net/~kakaroto/n810there are chinook and diablo files there.. they should work on the N800.. the newer tcl/tk won't work because it's not hildonized and the n800 doesn't have a hardware keyboard so that's an issue, that's why you need those packages..
there's only an old version of aMSN in there, but you could try to compile the new one yourself, just download scratchbox and compile it (follow the instructions on maemo.org, there's a simple script to get scratchbox and the diablo SDK).
Audio calls won't work though because the dependencies you need are not available on diablo and you can't install them (they would conflict with diablo packages, screwing up the VoIP features of the N800 itself).