I got 15inch PowerBook 1.33 GHz recently and it's fantastic and the most silent computer I ever had, all you can hear is hard drive spinning (which is also silent too).
Fan comes on only when I play games, but it's not a high pitch sound, it's quite pleasant
Laptop computers use LCD screens that have one native resolution (1280x864 on this PB) and although they can scale down resolution, it is a little fuzzy because the graphics card has to output picture of lesser resolution to a screen with bigger numbers of pixels, which makes it bad for reading and such.
But I think you'll be satisfied with whatever new mac laptop you get because they are incredibly more advanced and silent now, interface of Mac OS X has bigger elements, graphics, fonts etc. than OS9 which makes it much easier for reading and handling.
As for those loud G4's... Old PowerMacs were somewhat loud, depends on model, but I've tried new PowerMacs G5 and they are super-silent, they have 9 fans and you almost can't hear it.