the only real difference in mac/pc keyboards is the mac has command and options keys, while the pc has alt and ctrl keys...
and of course they are transposed... the mac's command key works as the ps'c ctrl key, but it is in the position of the alt key. same for the option and alt keys, they are the same, but in different locations on the keyboard.
i use both platforms daily, and the hardest thing to do is retrain my pinky fingers to hit the right keys.
other than that the keyboard shortcuts are the same in after effects.
option+[ (mac) and alt+[ (pc) both trim the selected layer's inpoint to current time; option+] and alt+] trim the selected layer's outpoint to current time.
however, this is for the us/english version of ae, other languages may be different.
here's the link to all the us/english ae shortcuts, if that helps at all:
http://help.adobe.com/en_US/aftereffects/cs/using/WS3878526689cb91655866c11...
Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW