Muiro, here's more about dependencies.
You have an RPM baseed systems. It means that the RPM database keeps trace of all installed programs. The thing is - only the ones installed from RPMs. It means, when you find an RPM which needs a library you don't have, you must install the library from its RPM, when you compile it from source, it won't work in 99% cases. For the database, the library was is installed...
So there's danger when mixing programs compiled from source and those from RPMs. It's one possible reason of dependencies problems. But not the only one.
You mentioned above that you had a dependencies problem - gtk was missing. But I'm nearly sure you had gtk installed at that time. Where was the problem? You had a part of gtk. The part that's needed to run programs using it, but not to compile them. The second part is called 'headers'. Headers are files in a programming language used to compile the program/library you have but also to compile programs based on the library. You don't need them for normal use, only when you compile.
Headers are usually kept in 'devel' packages. So a library has in fact two packages: 'library' and 'library-devel'. In your gtk problem, you probably had 'gtk', but not 'gtk-devel'. Devel packages for all libraries you have in RPMs are on your installation cds.
Now a short method to install missing dependencies. You compile a program. It fails saying it can't find something. First, make sure you have the library. Use the command
rpm -qa|grep something
where 'something' is the name you're searching for. The command above will list you all RPMs installed that have the string 'something' in their names. If you get a result - you have the library. Now look at the results again. Can you see 'devel' somewhere? If not, you don't have it installed and that my be the reason of compilation failure. So insert your installation cd in and start searching for package 'something-devel'. Install it and try the compilation again.
I am trying to get divx/avi's to work. First question, what program works the best in your opinion?
I prefer xine, it plays nice and I don't have codecs problem with it (they come in the package). I don't use such programs much, but that's another story.