If you want to keep using Sarge, you should create a preferences file in /etc/apt/preferences with:
Code:
Package: *
Pin: release o=Debian,a=unstable
Pin-Priority: 600
Package: *
Pin: release o=Debian,a=testing
Pin-Priority: 650
That way, not every package on your system will be upgraded to unstable, only those you select. It will always select testing packages first, even if it is an older version.
Then create a sources.list file that has both testing and unstable sources in it:
Then do:
To install a package from unstable (like kde 3.3.1):
Code:
apt-get -t unstable install kde
That should install kde and all required dependencies from unstable. Hope that helps!