There are several different versions of the Microsoft Natural Keyboard. The one I have (Natural Pro) as well as the hella-cool looking
Natural Multimedia Keyboard ($26+6 at newegg) have the inverted-T style arrow keys, and the old-style insert/home/etc. keys. I couldn't use ones with the rearranged configuration like Dave posted.
And to answer your question, no, you can't rearrange the keys. The ones that are next to the split are extra-wide to make up for the extra space.
After an adjustment period of about a week or less, you'll find the split keyboard much better. If you try to teach yourself Dvorak, you're just gonna be all f'ed up whenever you try to use someone else's keyboard, whereas with the split keyboard you can still participate in society with the rest of us.