Ok, there is some kind of psychological or brain disorder where the
person intends to respond in one way, but in reality they are saying
something else, but something that is strangely related.  The only
example I remember is this:

The patients doctor (or someone) says "have a nice weekend" and the
patient replies "Francis Gary Powers."  In his head, he means "you
too" but instead says the name of the pilot who famously crashed his
U2 spy plane.

I'd like to know the name of this disorder and, if possible, have a
link to some resource discussing the Francis Gary Powers example
above.

Thanks

The example that you've given sounds like an instance of paraphasia or
circumlocution. One condition associated with this kind of language
disorder is Wernicke's aphasia.

"Sensory (Wernicke?s) aphasia - lesions are located in the left
posterior perisylvian region and primary symptoms are general
comprehension deficits, word retrieval deficits and semantic
paraphasias. Lesions in this area damage the semantic content of
language while leaving the language production function intact. The
consequence is a fluent or receptive aphasia in which speech is fluent
but lacking in content. Patients lack awareness of their speech
difficulties. Semantics is the meaning of words. Semantic paraphrasia
is the substitution of a semantically related but incorrect word."

http://www.patient.co.uk/showdoc/40000746

I have a special interest in Wernicke's aphasia, since I once suffered
from it. Brain damage caused me to be unable to "find" the word that
would express my meaning, and I sought out a word that was somehow
associated with the target word. It was quite bizarre for me (and I'm
sure it was even more bizarre for people who had to figure out what I
was trying to say). The oddest example from my own experience: I
wanted to ask my neurologist's receptionist about paying the bill. The
word "bill" just would not come to my addled mind. Finally I spat out
the word "Donald" instead. Why? Well, Donald Duck has a bill. Somehow
this was not immediately obvious to the receptionist. ;-)

I don't know the source of your "Francis Gary Powers" example, but it
sounds very much like the sort of medical anecdote that I associate
with Dr. Oliver Sacks.

I agree with finkfreud-ga's 'diagnosis' of Wernicke's aphasia, here's
a link to the wikipedia site, the example they give is similar to your
anaecdote...

http://en.wikipedia.org/wiki/Wernicke%27s_aphasia