A "select Max(AutonumerField) from SomeTable" should be very fast even with millions of rows if it is the primary key. If it's not you might consider making it the primary key or at least index the field (use a unique index). This will greatly improve performance on this query and possibly others.
on the confirmation screen, if you are pulling the data out of the table, does this mean that the data is entered into the table before confirmation? what if the user does not confirm? don't you then have to do a delete? or are new records put into a temp table and then moved to a live table? or perhaps a status is set to "declined" or something?
in any case, max(autonumber) is not the way to do it, unless you can guarantee that only ever one person will use your application
as soon as multiple users can use the app, if you use max() you run the risk of presenting somebody else's row to the wrong user
what you should do is pass the form fields to the confirmation page, and use those values to query the record
after all, the autonumber is just a surrogate key, there should be other columns which you can use to uniquely fetch back the row