In order...

1. When I try to install various programmes (SuperKaramba included), it tells me that my KDE headers are wrong... what?!?

2. I installed a package which supposedly gave XMMS WMA playback, but now XMMS just crashes as soon as I add WMAs to the playlist. Why?

3. Again, when I try to install some programmes, it tells me that I do not have 'libgtk2.0-dev' installed. I checked on Synaptic package manager, and I dont have it. So I downloaded it from the Debian website, and it still can't install!

(Sorry there is so little information about problems 1 and 3, Ill get back soon with full details!)

The kde headers are kde development libraries. I am not sure what they are called on debian, but I am sure if you search for kde using apt-get or synaptic you will get the right package name. As for libgtk2.0-dev, I am sure its also available in your apt repositories. Anyway if not, you can install the package you downloaded using the command "dpkg -i package.deb". Can't help you with the xmms thing.