Some benchies showed 8800 gt sli to be better than an ultra actually.
But with the way these 9600gt's SLI are performing I'd go with that.
DUDE! seriously if your dad has the money to spend on an overpriced POS dell, he has the money to build a custom comp that will be your best friend ;D Tech Forums will walk you through what you should buy and if needed help you find the links. Putting it together is very easy, but you can be helped with that too if you need it.
But if your dad is still going to be thick then yes, that system will run most any game on max settings except crysis.