Would you like to go on a date with the guy you're good friends with? ie, do you fancy him? want to have a relationship beyond friendship with him? if so, then just go on a date with him... if not, then just go on the impression that he meant go out as friends, and if he does something that indicates that he likes you more than that, just explain to him gently that you appreciate him as a friend etc etc, but don't feel that way about him.
Don't lead him on, just be honest with him. Honesty always = the best policy. Believe me, it's bloody awful if there's a total misunderstanding and you end up in a situation that you really don't want to be in!