As others have said, you won't get a great gaming spec upgrade for £200. I can suggest this for a bit over:
Sapphire ATI Radeon HD 5670 512MB GDDR5 PCI-Express Graphics Card £65.99
(£56.16) £65.99
(£56.16)
Asus M4A78LT-M LE AMD 760G (Socket AM3) DDR3 Motherboard £57.99
(£49.35) £57.99
(£49.35)
AMD Athlon II X2 Dual Core 250 3.00GHz (Socket AM3) - Retail £51.99
(£44.25) £51.99
(£44.25)
Corsair Value Select 2GB (1x2GB) DDR3 PC3-10666C9 1333MHz Memory Module (VS2GB1333D3 G) £49.98
(£42.54) £49.98
(£42.54)
Sub Total : £192.30
Shipping cost assumes delivery to UK Mainland with:
DPD Next Day Parcel
(This can be changed during checkout) Shipping : £9.50
VAT is being charged at 17.50% VAT : £35.32
Total : £237.12
But you won't be running games released this year on high resolution with that.