personally i tried iScroll2 and found it pretty lacking. It didn't have the movement resolution i would hope for, so scrolling was jumpy and i had to fight with it. Course i look at things in terms of productivity. and since i mostly use a scroll mouse on my laptop. i don't need the extra software bogging down my system.
my two cents. as far as the scroll pad. You could probably cram it but you'd have to run it off of USB so if you can find a USB port (or pins is what i should say) you could put it in there. I'm not sure if the Tibook ran it's track pad off of USB or ADB. But i know from what i've read in the macmod forums that the Albook's track pad is USB.
hope that helps
macDeviant
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2.4gHz 15" MacBook Pro, 1.66gHz Core Duo Mac Mini, 2.5gHz G5 QUAD, 733mHz Quicksilver, 450mHz G4 Cube, 700mHz G3 iBook, 350mHz Sawtooth G4, 350mHz Revs. A and B B&W G3, 16mHz Powerbook 100, 8mHz Macitosh Classic.
If you installed W-enhanced trackpad, you should be able to run it with the Apple driver. I believe the trackpads in some of the later Alu PBs are just four pin USB devices. They certainly show up under the USB device tree in System Profiler. You ought to be able to use one via a USB port, the issue is if your existing pad is USB-based, or if there are any internal USB ports on the logic board you can use.