Yup, you're going to have to use an adapter. If you get a 2 molex to 6 pin adapter instead of a 6+2 pin then you might have to short the last two pins, so make sure to get thr right connector. Of course, if the GTS 250 has an 8-pin connector it's either an older version that sucks up more power or an overclocking version. Either way there's a good chance that CPU cannot handle it. If the PSU is really cheap you will hear a popping sound and see some smoke when you actually try to play any kind of demanding game.
Thanks for your reply guys, ive dicided to leave it and try to send it back and get a refund, if i dont then oh well but im going to save for a ATI 5700 or a ATI 5570, hopfully i dont mess that up either