Ok, done. Here's what I did (simplified version):
1. Install apt-get and Synaptic.
2. Add the Nyquist repository:
http://people.ecsc.co.uk/~matt/repository.html
3. Update lists in Synaptic and disable other repositorys.
4. Select Gnome upgrade packages and hit 'proceed'.
5. Restart X.
et Voila - Gnome 2.4!
Now I just need to get gDesklets working... will post that soon as well.