I've just finished building a Pentium 4, 3.0Ghz (Prescott) based system with an Intel D865GBF motherboard, 2GB DDR RAM (4 x 512Mb), a 30GB HDD IDE and a Winfast Geforce 3.
In fact, it flies along running Windows XP SP1 and I built it mainly because of skill-fade and to keep my hand in, as it were. The motherboard is top quality from Intel which I found from someone who lives in the south of BA (Glew) and it was worth the three hour return journey.
The rest of the components I had lying around, except for the case, which I bought cheap and it also contained a working motherboard (AMD Duron 1200), some memory and a hard drive. I also find it very relaxing, not to mention rewarding to bring all these old components to life.