[eluser]Krzemo[/eluser]
Just use sessions to store last submitted (and correct) form. I.e. if value of session var = 0 it would mean that user hasn't filled any form yet and because of that he has access only to first one. When first one is done, validated correct and saved to wherever you want to store it, change sess var to 1 and etc...
Needless to say that session var status check is a must before form page is displayed (and proper actions must be taken - i.e. redirect to last filled form page)
If you want your application to remember status between sessions you would want to store the status in db and use cookie or make users login. Simple as that...