if a new line of mac notebooks does come out this year, it will most likely be introduced in June because of WWDC. But i think its highly unlikely, because the macbook and the MBP are relatively new laptops...i dont think they will be replaced yet. Maybe some sort of sub-notebook or 15" macbook or something.
Seeing how the macbooks were "just" updated I doubt they will be updated again in June. I would say the Macbook Pros will be updated and possibly the Imacs. The Macbook Pro's might get the new santa rosa chipset and possibly the LED backlight to replace the LCD backlight. I would say that update will be at least announced at WWDC. Then the macbook will be updated some time in the first quarter of 2008.
There are rumours of the 13.3" Macbook pro also, but like i mention just rumours. No one here "knows", people are just speculating. But considering the macbooks just got bumped upto the Macbook pro performance (minus vid card) i don't see them getting updated in a month.