I'd also recommend buying an el cheapo multi-framerate player. Otherwise, the process is not trivial, although there's some good software out there which works. EG Canopus Procoder (very expensive). SUPER (freeware) might be able to convert the VOBs' framerate but then you'd need to create IFOs around the newly created VOBs (easily done with IfoEdit). Not sure how well the menus would come out, either.
You can also look here for some guides.
Regards