Or do you own the rights to any software you create, regardless of whether you used tools supplied by a third party?
You own the rights to the work that you have done. However if you create something that incorporates works created by a third party, then final software may have multiple copyright interests.
Some ways that the output can include works created by a third party would be that you've linked to third party libraries (wizards might have done this for you), you used a compiler that injects proprietary code into the output (there are a number of legitimate reasons that compilers may do this), or your final program output is a virtual machine image that incorporates other people's work (this tends to happen with image-based languages like Lisp and SmallTalk).
As a general rule, if any tool that you are using has the potential to inject some external copyright interest, it is in their interest as well as yours to make you aware of the issue. Therefore the licenses for the tools that you are using should raise the issue if it exists, and make you aware of the obligations that they feel you should have. Given that the tools you are using are intended for developing software, they are likely to make it easy to get around likely issues. Note that such licenses may come with lots of restrictions that protects someone else's interests. See http://social.msdn.microsoft.com/Forums/en-MY/Vsexpressvb/thread/7887e35a-d746-41a6-892b-22384c2278e9 for a realistically complicated example.
Note, I am not a lawyer and this is not legal advice. If you have any concerns after reviewing the licenses for the tools that you are using, I strongly advise you to consult a lawyer.
You own the rights to software you create. The XCode Tools and SDK License should be online at http://developer.apple.com, or can be found in