Whether AF does nothing for AH is a debatable point. AH doesnt make use of it, so it should do absolutely nothing. Any improvements are most likely placebo effect. But if the user feels its making an improvement, its up to them. However, more importantly is the warning that AF uses resources that could better be put to use rendering and can potentially cause serious gameplay issues with AH. And yes, it makes the text blurry.
As for the video card debate, 6600GT is the minimum Nvidia type card you should go with for AH. Prices are low enough on it that buying an older FX 5xxx series card like my 5900 is just silly, given all the shader problems those cards have in AH. If you DO buy a 5xxx series card, go with the 5900 or 5950. The others all have half the memory bandwidth and may or may not have used dubious parts to save money. If you go ATI, at the minimum I'd suggest a 9800 series card, the prices should be low enough that dropping down to a 9600 or 9700 should be negligible in price difference.
The above is merely my opinion, on the cards. If its temporary, buy whatever works for you money-wise.