You can fix your libxcursor-dev problem with this:
su
cd /var/cache/apt/archives/
dpkg --force-overwrite -i libxcursor-dev(your version here-just hit tab)

That will overwrite the problemed file. I don't know the answer to your kdelib problem. You can try the same command as above but put the kdelib filename instead of libxcursor-dev, but I can't say whether it'll work because I don't have that problem. I upgraded my KDE by removing the line in /etc/apt/apt.conf that make your default distro "testing". Now I just run debian/unstable.