Check the "Different odd and even" option (Layout tab of the Page Setup
dialog box)for headers and footers and then insert a page number for the odd
pages only.

So you want pages numbered as follows:
page 1 numbered as 1
page 2 not numbered
page 3 numbered as 2
page 4 not numbered
page 5 numbered as 3
page 6 not numbered
page 7 numbered as 4
etc.  If I understand the question correctly, then:

In Word 2003 or earlier, open your document, click on
File | Page Setup | Layout tab | check the "Different
odd and even" box | OK.  In the odd-page header or
footer where you want the page numbers to appear,
insert a calculated page number field:

{ = { = { page } + 1 } / 2 }

but do not type the curly braces; instead, insert each
pair by pressing Ctrl+F9.  When you've finished entering
the page number field, press Alt+F9 to switch back to
display of field results (the page number) instead of
field codes.