One way that would give you a good high end middle of the road is an ATX tower (£50-60ish) Supermicro P6SBA Motherboard (£60ish) a Celeron 533mhz (£70ish) and an Matrox G400 graphics card (£110ish) they all work VERY well together. The other peripherals are just a question of choice.
The board is good because it has USB and it takes the 66mhz Chip. Got one so I know. I've got a 533 now and it goes like stink.
Hope it helps anyway.