Does it really make sense with a 4200 X2 and a 7600GT? I'd spend the $200 on a new CPU or video card.
Also, unless you buy a high-end water cooling system, usually high-end air coolers exceed the performance of water cooling- and do it quieter at that (Radiators are LOUD).
$200 will not get you a watercooling kit that's actually worth it.
What are you looking to cool? CPU? GPU? RAM? All of them?
If you're only cooling the CPU, you can probably get something decent for $200. Look here for the best kits, I wouldn't buy kits from anywhere else: http://www.petrastechshop.com/wacoki.html
If you're going to make water cooling worth it, you have to know what you're doing when it comes to overclocking, you have to push your system beyond what air cooling can handle, and you have to buy the parts separately. Buying a kit won't get you any way near the same performance as if you bought parts.