Another system overload plea for help

Ive read various tweaks and suggestions but can someone simply tell me why LE would run fine on a 7 year old Power Mac G5 but on a three year old MacBook Pro it stalls at the beginning of every arrangement with the dreaded system overload error? I don't have either machine's specs handy but the MB Pro has 4GB of RAM and the PM G5 has 6GB. The MacBook Pro has an Intel Dual Core I believe and the PM G5 has a dual core PowerPC.

Someone might spare me from spending my spring and summer working in a hot upstairs bonus room If I can get the MacBook Pro to handle the loads. The pro audio buffer is set to over 1gB by the way...

Thanks