Arsing fucking crappy thing from hell.
1) Remove old KDE2 installation from Mandrake Linux - Good
2) Install new KDE3 packages - Good
3) Oooh, security updates for Mandrake, better get them as well!
5) LILO - Can't boot - XYZ too large
6) 2 hours later, after reinstalling the kernel whilst not reinstalling the whole darn OS...
7) Why isn't KDM working anymore?
9) 3 hours later - they called the session "KDE 3" which chksession couldn't parse! Renamed "KDE3" - works.
Was it worth it? So far it seems it is!