After several discussions on this point, please allow me to summarize what I've found (someone feel free to correct me if I flub...)
The Creationist term "kind" is objectively undefined and must remain so in order for the Creationist rhetoric to make any kind of sense. The main contradiction for Creationists in defining "kind" is to define this term simultaneously (a) broad enough that the observed instances of speciation can't be considered the creation of a new "kind" and (b) narrow enough that humans and the other apes are separate 'kinds'. In other words, at it's heart the word "kind" must fill these points in Creationist logic:
1. One 'kind' of animal cannot split into two 'kinds' of animals.
2. Humans are in a different 'kind' from the other apes.
But, as I've pointed out, Creationist rhetoric on this point only works if "kind" remains objectively undefined. Here is the sticking point: I've never heard any Creationist describe a test that definitively measures whether or not two animals are in the same "kind" or not.
For example, when I ask whether humans and apes are in the same "kind".
"We know that humans and apes are separate 'kinds' because..."
1. "They don't interbreed." (This would mean that current instances of speciation show a clear division from one "kind" into two.")
2. "They don't give birth to each other" (This would mean that human races are different "kinds", because Asians don't give birth to Africans.)
3. "It's simply obvious." (This is admittance that "kind" is simply a rhetorical tool, and is not an objective idea.)
The point here is that using the term "kind" is a rejection of the fact that life is organized into nested heirarchies, and that "kind" could mean any one of these levels, as long is it remains undefined. Biology already has a number of different systems for classifying life (Linnean, cladistics, phylogenetics, etc) and ALL of them lead distinctly to the conclusion that all life is related and descended from a common ancestor.