I'm not sure whether any of this will help, but here are my thoughts...
First, a quick
word on source directories: Source directories are those that Eclipse adds to the classpath in a project. Any
Java files you want to edit must be in a source directory (or a subdirectory, i.e., if 'src' is a source directory, class com.foo.BarClass would be in directory src/com/foo). One property of source directories is that they cannot be nested. I.e., if 'src' is a source directory, then you can't set 'src/foo' to also be a source directory. This is intuitive - if they were nested, how could Eclipse tell whether a class Bar in directory 'foo' is supposed to be in package foo, or in the default package in source directory 'foo'? (I hope that wasn't too confusing :-\)
In this case, the way to add a JAR is as you did in the first attempt: just dump the JAR anywhere in your project, and add it using project->properties->java build path->libraries->add jar. (this is the location in Eclipse 3.1, I think it moved between 3.1 and 3.0).
If you can't find the JAR, chances are you need to refresh your workspace. Also, I just ran a quick
test - JARs won't show up if you put then in a directory that you've set to be a source directory. Perhaps this is what you hit. If 'lib' contains only JARs (not .java files), then it shouldn't be a source directory.
I'm not familiar with Maven, so I can't help on the last point - but if you describe the functionality, perhaps I or someone else can.
-Tim