I'd recommend an intel Motherboard, with an intel processor. in order to get decent results, there is no need to go extreme.
an Intel D945GCNL Motherboard is a good board, and will run you about 100 dollars. do yourself a favour, and stay away from anything from MSI (Micro Star International)
as for the processor, dual core is the way to go. an Intel Core 2 Duo will run you 150 - 200 dollars depending on the speed.
I put a Saphire Radeon X1650 video card in my computer, and so far am very happy with it. it ran me about 100 dollars. Again, stay clear of MSI
beyond that, a SATA Hard drive is always a good thing, 500 GB is a good size and runs less than 100 dollars. As for networking, I have had the best luck with Linksys, but others swear by other brands, they all cost about the same.
hope this gives you something to chew on.