You can try:
Code:
nano /etc/apt/apt.conf
and see what it says for default release. If that file doesn't exist, try:
Code:
nano /etc/apt/sources.list
and see if the sources are for "stable", "testing", or "unstable".
It looks to me like the error is because you are using xlibs from stable (version 4.1.0), but the package requires xlibs version 4.3.0 (available in testing). If you add testing sources, you can install the file. If you make your sources.list file look like:
You will have testing and stable sources. After running:
the testing packages will be available to install. If you then run:
Code:
apt-get install x-window-system
it will upgrade your X windows from version 4.1 to 4.3. If you then run:
Code:
apt-get install tk8.3-dev
it will also install the required files from testing.
Note: If you do what I said above, any time you install new software, it will automatically come from the "testing" branch because packages are newer versions than stable. If you prefer to keep most things stable, you should read about pinning:
http://jaqque.sbih.org/kplug/apt-pinning.html