the best way to do that is using cookies, it's very easy to use them with php , you'll need to make an array of cookies using something like that.
in some page you ask a question number1
do u like chocolate?
i answer yes (with a radio buton)
then you send the variable of the form to the response page with the answer on a varible called eg: radiobutton1 with the value yes, ant put that line at the first line of the action page
setcookie ("answer[1]", "$radiobutton1");
it will set the firt element of the array with the value "yes"
you can acces to this cookie just caling to the array.
print answer[1];
it will print "yes"
you can do it several time doing assingments to your array several times and accesiong it via its name.
do you like coke?
no ( you asign it to radiobutton2)
setcookie ("answer[2]", "radiobutton2");
and you acces to this value
print answer[2];
you can do a mark beside the the ansewer with an statment like that
if (answer[2]=="yes"){
print "you answer yes";
}
check out this page for more help you will there a lot of options for cookies, because my examples are just raw code build on fly for you
http://www.php.net/manual/en/function.setcookie.php
the best way to check if the all the questions are answered its using client-side javascript you will find a lot it must be somethin like that (this check the length of the string i don't know the method to check boolean data but you can find it at the web, or find a better function, i'm not a javascript guru and i can't help you so much with it)
function validation {
if (yourform.yourinput.value.length > 100)
{
alert("Your text must be shorter than 100 chars.");
yourform.yourinput.focus();
return (false);
}
}