'k Don... go to your room.
Colin, if the problem recurs, a way to kinda-sorta pin down what's at fault (Rob's explanation of increasing resistance with increasing temp should NOT be taken lightly) is kinda tricky. It requires two folks in sympatico:
One to turn the key (for no MORE than two seconds at each attempt) and one to WHACK th' starter motor case unerringly with at least a 10oz hammer AT TH' SAME TIME. Repeatedly, and in a staccato rhythm. If you can find an accomplice to help you DO this, as you strike the starter motor and it suddenly spins normally the starter is at fault. It can usually be a simple matter of replacing the brushes and cleaning the commutator. Otherwise it'll mean a starter replacement.
Who says there's no VOODOO left in th' world!?!?
...I know it sounds... err... whacky... but t'is th' truth.