Swiftech Apogee blocks, a Laing D5, 1/2" Tygon tubing, Feser One additive, and a Thermochill P120.3 radiator would be the best you could get for an easy build right now.
The Swiftech MCW60 is more than enough for a GeForce 8800 processor,
but the video Ram will do better with a full coverage block. The 9800 GTX seems to have PhysX built into it, and can be bought from BFG with a Danger Den full coverage waterblock standard. It's called the 9800GTX H2OC. Using one of these could simplify your system a little and get you a real warrenty. (none of the 'warrently is void, you took off the heatsink' BS)
Personally I wouldn't recommend getting any Koolance blocks, as they tend to mix metals, which can cause galvanic corossion. It might be a better solution to get Mosfet/Ram heatsinks and put a very low speed 120mm fan above the MB to cool the voltage regulators, northbridge, and southbridge; they use very little power.
Using three radiators will produce more flow restriction than using one made for three fans. I recommend the Thermochill P120.3, as it is optimized for low airflow. If you use something similar to Swiftech's Radbox
You can mount the radiator outside of the case, although you will have to make some holes for the tubes. Oh, and don't forget a shroud. A shroud will drop temps slightly and decrease noise.
Your CPU temps may drop 5c, my Q6600 hovers around 15c above ambient when idle with OCing. I can't be sure, but your GPU temps could drop about 10c idle, maybe 15c load with the 8800. The 9800 GTX H2OC would be about 60c - 65c in Speedfan. (mine is) Motherboard temps are harder to predict, maybe about 35c? MCP temp will likely drop with a little extra cooling too.
The actual loop itself doesn't matter much, as long as the reservoir comes right before the pump. That usually makes it easier to fill the system.
Oh, the D5 has a very high pitched whine to it. The whine can be largely removed by elastic suspension, or by placing it on soft foam. Some models of the D5 have speed control, I would recommend one, as the D5 is overpowered for PC cooling. I only run mine at about 66% of full power normally.