Can An Apple iPod U2 Special Edition (20GB, second generation) Charge By Computer??? ?

I Have An Apple iPod U2 Special Edition (20GB, second generation) And When I Tried to Turn It On It Said I Needed To Charge It From The Wall.But I Only Have A Computer Charger So Im Having My Friend Charge It With His Wall Charger And Now Im Wondering If When I Get It Back If I Can Charge It By The Computer?Please Answer