i agree that if RAB is reg black then it makes sence the kreacher would go with him and it also makes sence to me that the reason kreacher is so crazy is because he drank the potion.

but......

what i want to know is how did RAB know the horcrux was a locket because he either new it was a locket and took the fake replacement with him into the cave at the same time,

or he stole the horcrux then returned to replace it with the fake one.

now i know it sounds a bit stupid wondering weather he replaved it at the same time or after the fact. but it makes me wonder weather this RAB had a pensive or somthing aswel because it took dumbledore all this time plus slughorns memory to work it out properly and even if RAB was at one piont a death eater i still dont think that voldermort(sp?)
would ever tell anyone......
so how the hell did this RAB:

1. find out about the horcrux's
2. know where to look
3. have enough time to steal the horcrux then return to replace the it with the fake locket (because in the note in the locket i thought it said somthing like RAB would all ready be dead by the time vold finds that it has been stolen and if so then who was after RAB besides vold because vold couldnt have killed him because he's suposed to be dead long before vold even finds out that his horcrux gone)!