Sorry, but not letting your underage son/daughter stay out overnight with people you don't know is not really being overprotective.
This is true.
Once you turn 18, you can expect that your parents will be a bit more liberal about these sorts of things. Until then, sorry but you'll just have to go home at midnight (unless you can somehow convince your parents otherwise).
But seriously though, going home at midnight isn't even that bad. Most people will probably be burnt out by then so you won't miss out on much. Infact, you will probably enjoy your sleep more when you are in your own comfortable home than on the hard floor of a friend's house.
I don't know how old you are... I'm assuming about 16-17. Either way, it won't be long until you become an adult, get a driver's licence, go to university and get more freedom to do things like this regularly. All in due time, my friend 
haha no im 18.
ive been 18 for a few months actually
i dont know what to say them, all the suggestions made so far ... dont seem applicable.
ive tried the main points already and nothing seemed to work!
grr
theyre definitely aware of what happens at 18ths, and they probs dont care about that stuff.
its more the fact, they dont know my friend. (they dont know many ppl from school actually...), and so their line of argument is that, i cant sleepover, because they dont know my friend, what type of person he is. theyre also against the fact that this particular house is not his actual residence, its a rental property in town that is currently vacant.
im in a pickle really, i think i haven't got much 'a charnce' (haha get it, a charnce.... a char .... achar? )