Just to be devil's advocate, i have to mention Intel chipsets here.
Now, i am not an Intel fanboy, even though my current system is a P4, but Intel chipsets are renowned for being rock solid. Sure, the CPUs are not considered to be best value for money / performance, but if rock solid is number 1 priority you'd be silly to ignore it.
Try this 945 chipset-based motherboard, for £79, plus this Dual core P4 for £175.
£250 for a dual-core system that WILL be rock solid, can't be ignored as an option.
That said, i'll probably be getting an AMD system for my next upgrade