Screen recorder

I know this has probably been asked a million times, but does anybody know of a free screen recorder that works well with games and won't make me lag?

my computer is shit and I want to record.

Don't bother mentioning any that only let you record for 30 seconds I need better than that! thanks in advance

If you don't have a good PC no recorder will work well. If the footage isn't meant to be edited and used for montages you can try xfire (crappy quality but smoother than others).