your harddrive is an ok size, you need ram. cheapest money can buy is around £30 a stick for 512.
2x512=1024=£60
graphics... an ATI X1600 will do in 256, thats about 60 squid
and £80 for a new P4 processor. assuming the motherboard supports it. motherboards are dirt cheap however for the non-amazing ones, look at my earlier post about a website miss pricing, i got a very high performance motherboard for £30. your £200 is easily reachable, dont listen to these goons. ill even give you websites where you can find these prices.