All you need is a 6pin to 6pin firewire cable. (if you haven't already got one)
Shutdown the powerbook, and keep the iMac on, then connect both macs together with the firewire cable, then boot up the pb while holding the 't' key down, and your pb hd will pop up on the imac's desktop. (all of this is explained in your powerbook's getting started manual)
then all you need to do is copy the files over.
with itunes and all you should need to do is replace the 'itunes' folder in 'music' in your users folder with the 'itunes' folder in the same place from the imac.
same with iphoto, just replace the 'iphoto' folder in 'pictures' in the users with the one in the same place from the imac.
but if you've got any music or photos on your pb then back em up first or you'll loose them.