how much is it worth?

i am wondering about how much my ocmputer would cost "4 months used", i made it over the summer and was interested if i should sell it and make my self a newer better one, its a intel 2.4ghz, 512 mb pc3200 ram, radeon 9600 pro,40gb hd, 20gb hd, custom case, 1 cd/rom, 1 cd/writer, 450watt psu, windows xp already installed, microsoft 2003. any suggestions would be really appriciated thanx, tell me if u need more info