OS X 10.1 to Jaguar Requirements

I have had OS X for some time now and ive upgraded it all the way to 10.1.5 and it ran great with little gui lag and so forth. Well i just got jaguar and now it lags all the time and i got a cpu measurer in my menubar and just playing itunes uses up %50 of my cpu NOW! Does anyone know why this might be? Does jaguar have that much more "behind-the-scenes-calculating" to do that its 10.1 friend? The only big differences i know of were some knew applications and tools like inkwell and rendevous....then quartz extreme.......i thought maybe they didnt optimize jaguars gui for processors since its meat to be handled by AGP graphics cards now.... well guess wqhat i dont hae an agp , but pci...and i dont have an agp slot eitehr........another question? Can i get a new motherboard to fit into a G3 blue & white tower with agp? Ok im done.....