Glad to see you doing some searching !! And I'm glad things are starting to come together on your system. I would agree that building from source is your best bet! But from your comments it looks like your attempting to build the src rpm. What you want to build is the original source from the person / group who wrote the program.
Some notes:
Slackware is not an rpm based distribution. it has rpm installed but it is not really functional. Any rpm you install will give some dependency error because rpm maintains a list of installed rpm's and compares them to the dependency list of the rpm you want to install. Since Slackware is not rpm based you don't have any rpms installed and there fore no installed list (rpm database) to check against. This does not mean that you don't have the program/lib that rpm is complaining about. It just means its not in the RPM database. Here are some paths to go down to install this software.
rpm2tgz : This tool creates a tgz (standard slackware package) with which you can use the installpkg program to install and see if it works. Since there is no dependency checking in Slackware this may work or it may not?
man installpkg
linuxpackages.org: see if what you want to install has alreay been converted into a package.
here are a bunch of Slackware package management tools.
http://freshmeat.net/projects/pkgsummon/
http://freshmeat.net/project
http://freshmeat.net/projects/slackpkg/s/slaptget/
I have never used any of the above tools! I almost always build from source or use linuxpackages.org.
I use GNUStow to manage my packages.
http://www.gnu.org/directory/GNU/stow.html
Hope this helps don't get too discouraged its worth it.
-Matt