Page Up/Page Down keys using left hand only?

I use the page up and page down keys a lot if I am browsing online or using Word - but I have to hold down the "Fn" function key to use them, making it an unweildy two-handed job. I'd like a way to use page up/page down and still have a hand free to use my trackpad.

Is there some script or preferences window that can make other keys act like the page up or page down keys (for instance ctrl-A and ctrl-Z) or are keyboard keys locked into only doing their original purpose?

ibook g4 Mac OS X (10.3.9)