Welcome to the forum!
The all in one kits like that Thermaltake are just as easy to install as an air cooler, but are usually more expensive for their performance. I really don't recommend them except in very specific circumstances, you're better off buying a good air cooler. I would pick up something along the lines of a Prolimatech Megahalems, Thermalright Archon, HR-02, True Spirit or Silver Arrow, or a Phanteks TC-12 or TC-14. All will perform on par or better than any all in one "water cooler" and will cost less.
The P5Q3 doesn't support SLI, so you can't get another 9600GT to run together - even if you could, I wouldn't recommend it, because they're old cards now and even in SLI, they're not very powerful by today's standards.
What power supply do you have? Any graphics card upgrade recommendation will be based on that, there's no point recommending a power hungry card if your PSU is low powered or low quality. Also, bear in mind most modern cards will be bottlenecked by your CPU, but you'll certainly benefit from an upgrade over that 9600GT as that's really holding you back. What resolution will you be playing at, and what games?
When you say you need better RAM - define "better". Do you just need more RAM? Faster RAM?
Finally, do you already have an SSD? If not, I would personally make that my top priority and pick up a Samsung 840 (preferably the Pro or Evo rather than the Basic), Crucial M4, or a Plextor SSD, because that'll make the most noticeable difference to your PC's everyday performance.
Edit: oh, an overall budget would also be helpful
