Here are the rumors:
1. The iBook is now MacBook and is in a 13.3″ widescreen form factor
2. The MacBook will ship in white and black and will cost slightly more than the iBook
3. Apple announced an iBook event to announce the most affordable iBook ever
So if we combine these together we get my WAG:
Tomorrow Apple will announce the 13.3″ MacBook in aluminum, the little brother of the 15″ and 17″ MacBook Pros and will also announce the new Intel iBook line that come in white and black, also with 13.3″ widescreens. The MacBook will cost slightly more than the current iBook while the new iBooks will cost slightly less than the current iBook. As for specs, the MacBook will start at a 1.66 ghz Core Duo, while the iBooks will come with Core Solo processors.