Thanks for the quick reply Stormy, I can definitely understand that being the reason why its dropped. I did have my worries that i might have been buying the wrong card, but from reading the specs from the one i got, it just seemed like it was better than the 4850. It supports DX 11, runs on open GL 4.2 and has 2 GB memory. (Mines a Zotac GT 520 so its not exactly the same as the one on the nvidia site) and the 4850 only supports DX 10 and is a lower open GL version also with only 1 GB memory. As far as everything else goes (graphics clock, processor clock etc) my GT 520 is higher in spec than the AMD. I made sure all the specs were atleast slightly higher before buying it.
Here is the exact one i bought in case your wondering on the spec difference.
(I think it actually is a GTX but the box it came in only says GT, as it does on the image in that link)
ZOTAC GeForce GTX 520 Synergy Edition 2048MB GDDR3 PCI-Express Graphics Card [ZT-50605-20L]