Shouldn't matter what way the radiator is. As long as air flow is going through it. i would suggest however you get one designed for PC water cooling as they are pretty cheap these days unless you just happen to have that heater core laying around. Also make sure it is copper brass not aluminum.
As for a rez however you want to go. They have cheap plastic ones that fit in the bay for like $12.
http://www.dangerden.com/store/produ...1&cat=6&page=1
If you make your own make sure it is copper and/or brass. Personally I just drill a hole in my radiator and solder on a fill/bleed tube and use that as the rez. Swiftech has a new radiator/rez out also.
http://www.heatsinkfactory.com/swift...reservoir.html
Water block... If you want to do it yourself go ahead. Drill holes and connect the dots.
http://www.procooling.com/index.php?...icles&disp=128 Will not be much more just to buy a good commercial one though. Even on e-bay for dirt cheap.
Pump. DD12V-D5 Pump Variable Speed is good. Can adjust the RPM for noise/performance.
Tubing I prefer 3/8"ID min and 1/2"ID max. Anything over 1/2" tends to kink to easy. Anything under 3/8 maybe reduce flow to much however 1/4" will work but most blocks are setup for 1/2".