Ursula,
I use to do that using the view Edit in Datasheet. Make an Excel Sheet with the same columns as the Datasheet view and then make a copy-paste. If you have some people field or lookup or lists, be sure you are pasting the same name as in the connected list. Anyway, if you have some diferent name, while importig data you'll receive an error of how many fields doesn't imported correctly.
Best regards,
Albert