You can also substitute a reservoir for a fillport/T-line. You have to check it/top off more often than a reservoir but they look pretty slick.
Here's a picture of the fillport, I cut a hole through the case (forgot what diameter) and bolted it on.
Here's another picture of the finished loop; yes I know it looks bad and the loop length is way too long, but the GPU block I was using at the time had bad barb placement
. I mixed the water/antifreeze in a bowl then used a plastic syringe to put it in the fillport opening.
I agree with Demigod on the pump. The D5 is an excellent pump, some people also like the Laing DDC as it's a bit smaller and has 3/8" fittings instead of 1/2" for the D5. If you do go with the DDC, there's a variety of replacement impeller housings that make it perform better.
Now for tubing... I prefer 1/2" inner diameter myself, but 3/8" should work okay as well depending on what you'll be adding to the loop. Are you just going to cool the CPU with it, or GPU/chipset as well? The only tubing I used on my system was Tygon R-3603, which is very nice but is fairly expensive by the foot. I've heard good things about Masterkleer tubing and it's quite a bit cheaper. Both brands have tubing in 3/8", 7/16", and 1/2" ID sizes.
As for fittings, I used Danger Den's
Perfect Seal fittings and they worked very well. It's a bit harder to get the hose on with those, but they seal very well. Some people have even used them without clamps, but I don't recommend doing that.
For the coolant, I used a mix of 90% distilled water and 10% antifreeze (usually Pentosin G12). For water, distilled is key. Tap/regular water is ionized and contains minerals and other crap, which can corrode the radiator interior/fittings/waterblock and makes it electrically conductive. I had one of my hoses pop off and spray water everywhere (due to my maintenance laziness), yet almost all of the computer survived it even when I tried turning it on a couple of times after the incident before I realized what happened. If I had used regular water it would have been screwed. The antifreeze additive is also non-conductive and acts as a "water wetter" as well as helping prevent algae growth.
As for everything else, read Demigod's post
.
Edit: Damn, after writing that I have the watercooling itch again. Maybe once I rebuild my Socket 939 rig (the one that I watercooled previously), I'll do that again to it. I still have all of my parts so it should be pretty easy to do again. I just need to look for a not-so-huge case that'll accommodate a dual 120 radiator.