'Playable' settings vary between people. Halo will run badly because it's a badly written steaming turd of a game anyway (IMO of course). If it doesn't run well enough, then reduce the settings until it does. I would suggest AA (AntiAliasing) and AF (Anisotropic filtering) be the first things you turn off, if you have them on. I would expect 1024x768 with medium to high settings would be very smooth with the games you mentioned, but at the end of the day you just have to fiddle until you're comfortable.
A 9600 series card is far from high-end these days, so don't expect it to run modern games at high res with all the eye candy. It just won't.
If it didn't (originally) come with a fan, it's fine, unless you live somewhere with a stupidly high ambient temperature (death valley?) or something. It's been designed to function out of the box, as is. If you desperately want to attach a fan, Most aftermarket ones come with a straight-through molex connector so it would plug directly into the power supply, not the graphics card itself.
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<font color=red>"Life is <i>not</i> like a box of chocolates. It's more like a jar of jalapeńos - what you do today might burn your a<b></b>ss tommorrow."