Hi,
This error message means you need both files to install the rpm you want to install. I recommend you do this: go to
www.rpmfind.net and look for
libnewt.so
libslang.so
You will get a list of rpms that have those files (maybe two rpms, one for each file).
You may also get a lot of possible rpms there containing those files. Pick the one that seems the best fit for your distro. Also check that, as linux runs also on other computers ("architectures") besides pcs (pcs are identified as "ix86" , where x is a numbre from 3 to 6) get an rpm with ix86 somewhere in its name. If you get the wrong one, it will simply refuse to be installed, so dont worry, you cant break anything.
Examples of other architectures are PPC and sparc.
Hope it helps,
-- Gway