I can't imagine a scenario where it would be worth putting a liquid cooler on such an old CPU. Anyways, a Be Quiet! Silent Loop 280 or Corsair H100 (not H100i) are good liquid coolers with LGA775 support.
I hope you do realize you can sell your QX9650 for $80 to $100 on eBay. Depending on the motherboard. You can likely get anywhere between $50 and $130 for your motherboard. Plus $10 to $20 for your RAM. Depending on how much you have.
If you add all that to the cost of a good 240+mm AIO liquid cooler. Let's say $120 to $150. You'll have a total budget of $260 to $400. In either instance you can get a modern CPU, motherboard and RAM. Which will dominate that QX9650. Even with a maximum overclock on the QX9650. A lowly Pentium...