Tonar, the 8600 is crap......don't even consider it. The 9600 might be worth a gander though. I've heard that some of the 8800 GT's are going for $150 or so - serious bang for the buck. The mini ATX should go into your case fine, but it will be cramped. I would be hesitant to buy an aspire power supply, see if you can get a Thermaltake, antec, corsair or something along those lines, if you look for sales you can get a good price.
My best advice is to be pacient, you've lived with your present computer this long, a couple of weeks of research won't kill you. You will have to live with any mistakes much longer than that.
PS I'm really sorry if I sound like your father, it's old age setting in and I really can't help myself.