swap the hard drive to a seagate 500gb 32mb or a 640gb WD. since this is a gaming rig get vista for dx10 and 4gb of memory gskill is good (corsair will do if dont sell gskill or ocz reaperX). get a ds3r gigabyte p35 motherboard will is a bit cheaper.
i dont know how much things cost in relation to usa but you should be able to get a better graphics card like a 9800gtx or gx2. but of course it should pay of to wait for the gtx280 and 240 will should be out very soon