As this thread gets more and more off topic, I'll take the wheel of the bus and bring us outta the forest and back on the nice gravel road....
<< And what does it mean when it says "64 mb integraded shared video memory" >>
Basically, it means that the video card is directly off the motherboard, and shares system resources.
As for where to get parts, try a few local stores. More often than not, they'll either price match what you can find on the web, or have the same price and save you some S&H (although Tax makes up for it)
Just make sure that you get a motherboard that gives you room to expand (atleast 5 PCI, 1 AGP slot), and with a high power Athlon, DDR RAM (Either Crucial or Mushkin).
As for HD space, usually 30-40 gigs is more than enough, unless you plan on doing some hardcore 3D moddelling and video editing, in which case I would say switch back to your Mac.
Video card: If you don't want to spend too much now, get a motherboard with integrated video that also has an AGP slot. That way you can upgrade it in the future.
RAM: Win9x - 256
Win2K - 256 or 512
Lots of other stuff to consider, like Burner or DVD, but just look around on the forums. Go to the Hot Deals forum and see whats there, usually there is some good stuff posted.
Hope this helps. If you have any other questions, feel free to PM me.