Even if a store did fit watercooling for you that wouldn't mean all the tinkering was done with.
What would happen if you encountered a leak, needed to drain your loop to change a component, had to replace part of the loop itself etc? It's rarely a good idea to watercool without the supporting knowledge to deal with any potential upsets it may (will) cause in the future.
Furthermore, why do you want to watercool? Based on what you've said so far (i7 from 2.66 to 3.2ghz) I find it hard to imagine that you have a reason outside of either aesthetics or the kudos of having a watercooled PC.
The other reasons for going down this route are usually for attaining overclocks that aren't feasible on air cooling, or, to keep things as quiet as possible (this is why I do it). Taking a 2.66ghz chip to 3.2ghz can be done quietly on air cooling anyway without anywhere near the effort, knowledge or cost of involving water.
Oh and a custom loop is simply a watercooling system which is made of individually sourced components, rather than an all in one solution such as the Corsiar H50, Coolit ECO or asetek LCLC.
If you're still serious about water then I'd recommend going away and doing some reading to give yourself a working knowledge, then coming back and asking specific questions to fill in the gaps. I know this is a more effort than saying "spec me water" and having somebody rattle off a shopping list along the lines of "DDC, heatkiller, PA120.3 etc etc" but it will serve you better in the long run.
