The same in meaning-- though specialized exceptions will arise (no
doubt, later in this thread). The phenomenon is fronting of the
negation, which we have discussed elsewhere (and which will require
Paco in order to locate). The effect is the carrying of the
negation to the main verb (
suppose, believe, think)-- but, interestingly, doesn't seem to work (at least for me) with
guess:
I don't guess sounds odd to my ears; perhaps it is an anomalous exception?