Publisher is probably not your best choice for this as it does not directly
support dynamic features, and is probably best used for static sites.
However you can use the Insert HTML code Fragment feature to insert scripts
that might do what you want to do. Check with your webhost to see what they
offer in terms of merchant services that could be incorporated into your
site, and go to David Bartosik's site to get his recommendation on who to
use. Look in the right hand column:
http://www.davidbartosik.com/
Also go to
http://www.publishermvps.com/WebDesign/tabid/29/Default.aspx
and you will see a list of Publisher built sites, some of which are doing
what you want to do, and be sure to read the material in the left hand
column. Again consider switching to more appropriate applications such as
FrontPage for building more sophisticated, dynamic websites. You may invest
a lot of time trying to use Publisher only to need to switch at some later
time.
DavidF