I dig the airconditioner blowing on the radiator...that should be able to give you some nice temps.
As for the pump, if your looking at one or more heatercores with a MCW5000 and a GPU block at decent head, your going to need something a little more hefty methinks.... The VIA 3000 is only listed for 6ft head, and isnt known for great pressure overall anyways so for higher performance I would look for something else. For a decent price you can check out a Danner Mag3 or Mag5 from local aquaium or petsmart stores, but if those are too expensive for you, then maybe the VIA is the way to go.
For heatercores, there isnt any need to go pulling apart cars, you can just find some at any decent auto parts stores in your area. You will most likely have to ask for them at a counter so they can get them for you in the massive rack of parts that they store in the back. Another option for heatercores that I have taken advantage of are the "premodded" heatercores at
www.dangerden.com (listed under radiators->heatercores). They sell nice and clean single and dual 120mm heatercores with mounting equipment which makes things very easy. No gunk or fittings to worry about like you would for ones pulled out of cars. Ebay is also a good place to look for heatercores, but I would really recommend dangerden for no mess no fuss etc...
A good GPU block for that 9800 would be the Maze4 by dangerden, or the GPU block from swiftech. Either one would work very well. I have a Maze4 GPU on my 9800P and it keeps it nice and cool while not killing a lot of flow. Keeps it at a nice overclock too

As for your question about whether you should or shouldnt cool your video card.... Its up to you. Personally I love it, but overall it doesnt really make much of a difference for typical users who dont push every bit of performance out that they possibly can. Personally I would save the money on the GPU block to save up for something more important in the future (next gen video cards, a nicer pump, etc.. etc..) rather than adding an extra block to a system with a bit of head and some possible flow issues as it is...
Hope this helps. Good Luck!
-OMP