"Does how likely my opponent is to have flopped a certain type of hand affect how likely he is to have that hand when he represents either it or another hand equally, all other factors withstanding?"

Edit: Adding an example I gave to a friend over MSN:

Like, if somone stuck a gun to your head and said "your opponent must have either 77 for a set or AK for a pair, he's equally likely to be dealt either 77 or AK (not the case in reality, but assume)" you'd choose AK and expect to be correct by a large margin?