Yeah, okay - the instructions on that site are the annoying way to do it. Especially this stuff:
Package: *
Pin: release a=testing
Pin-Priority: 650
Anyway, the easy way is as follows:
1) add a testing or unstable source to your /etc/apt/sources.list (e.g. this: 'deb
http://ftp.us.debian.org/debian testing main non-free contrib')
2) run 'apt-get update'
3) run 'apt-get -t testing install kde' (replace 'testing' with 'unstable' if you used that).
4) done.