Either use a 2 x 2 table or create it at full size and print four pages to a
sheet (zoom setting in the print dialog) - see
http://www.gmayor.com/print_multiple_copies.htm

The easiest way is to select Avery 5845 (Note card) as the "label type" in
Tools | Letters and Mailings | Envelopes and Labels | Label Options. On the
Label tab, click New Document to get a full sheet. They're set up as a 2x2
table, so be sure you have table gridlines displayed (Table | Show
Gridlines) so you can see the card boundaries.

You could set up a 2x2 table yourself, as Graham suggests, but using the
label definition is better because Word has already taken care of the page
margins and built in some sort of "magic" that suppresses the "Margins
outside the printable area" error message.