the airport express would give you a wireless base station to share a usb printer (check to see if your printer is supported) and your internet access (via ethernet) with macs and pcs that have wireless cards
http://www.apple.com/airportexpress/
the macbook has built-in wireless (airport extreme)
if a mac hasn't got a wireless card built in then you'll need to add one, apple has two: 'airport card' and 'airport extreme card'; older macs take the plain airport card, newer ones take the extreme version, there are also third-party wireless cards available for macs with standard pcmcia/pci/etc. slots and for pcs
