My suggestion would be to use hidden form tags.
You could use sessions I suppose, but the session can time out in your guy get's up to watch television while it's on the confirm page 😉 ....
You could also write to the database in the first post and set a flag field in your database to true if it's accepted, etc. but that's just alot of unnecessary extra work.
Hidden tags work well (watch out for situtations where you can set a variable twice. Like submitting the form to itself, for example. You don't wanna end up with:
<input type="hidden" name="firstname" value="bretticus, bretticus, bretticus">
So you just do this on your confirmation page (apart from displaying what they have submitted.)
while (list($name, $value) = each($HTTP_POST_VARS)) {
print "<input type='hidden' name='$name' value='$value'>\n";
}