I might be missing something here, but won't it be easier to simply send the entire form through once (form 1 and 2), and see if entries in form 1 validate.
If they do, go ahead and process the forms (email, add to database, whatever). But if form 1 entries do not "validate", simply return back from your script displaying an error on the resulting page. The user can hit back and correct the entries - then resubmit.
Is there a reason why you can't send the info from the second form when you send in the first? You don't have to do anything with the information but why can you not just send it along and leave it alone unless the first info checks out?