If you like the Gigabyte ATX UD boards but are not fussed about DDR3 maybe try:
Gigabyte GA-MA790GP-UD4H (790GX + SB750 Chipset, Socket AM2+, AM3 CPU compatible) (£97.74 + £9.00 del) which also works with your P2 720 and should overclock it with ease.
4GB (2x2GB) Corsair TwinX XMS2 CAS 4, DHX (
£50.19 or
£39.84 if the CAS 5 will do)
Samsung Spinpoint F1 640 GB is about the best bfb atm (
£49.98) - about 7.8p/GB (although 1TB F1 can be had for ~ £75 or 7.5p/GB on
Today Only at Scan)
With the money saved (£34-£44) consider the (faster?), quieter, cooler, more efficient Sapphire ATI Radeon HD4870 Toxic 512MB (the one with vapor-x) -
£172.49