Best as I know, changes within a species has been explored and well documented. That aspect of evolution is solid.
A change from one species to another hasn't been proven, though.
Don't use the word "species" as it is really meaningless.
See http://www.nwcreation.net/wiki/index.php?title=Macroevolution
The problem is that the words used popularly aren't particularly meaningful in scientific contexts. Creationists believe that organismal forms are fundamentally stable even through change, and that is probably a better way of putting it.