You may need to spend a few more quid. Don't cheap out on the PSU. Under sized PSU's that fail tend to destroy Mobo's. For this system I would go with no less then 650W Bonze 80. That's assuming one GPU and one HDD.
+1 DON'T cheap out on the PSU. A GOOD 600W PSU will power that system just fine, but 40 to 45 quid probably won't get you that.