PowerBook - Help with some Xbench Q's

I have read a few threads about Xbench on this forum and a few others and i was wondering what exactly it is and what are some average scores for my comps.?

I have a 1.33 ghz 12 inch ibook with a 60gb hd, 1gb of ram, and a combo drive

My other is a 1.67 ghz 15" Powerbook with a 100gb hd, 2gb of ram and a super drive.

Are you supposed to run this test after a clean install or with all the programs and stuff on the computer? Thanks for your help and pateince.