Well like Big B said, if you keep waiting for the next card, you'll never buy one.
As for the XT versus the AIW, they're not comparable imo. One is the fastest card, pure and simple, and the other as all the bells and whistles, as well as being very fast.
Since you're considering those two, I think we can fairly say you don't really need the AIW functions. that, plus the 9800 XT is not extremely faster than the 9800 Pro, so I'd just get that and be happy with it. It's a very fast card, believe me.
Of course the best deal is a flashable 9800 non-pro but luck is involved so if you're on a budget, forget that route altogether.
In any case, if the price difference between the 9800 Pro and the 9800 XT is bigger than the price of HL2 ($40 ?), then go for the 9800 Pro, else, go for the 9800 XT.
As for the future, look at the 9700 Pro. It's been around for more than a year right ? And it's still one of the fastest cards out there. I'd take it over a 5900 Ultra anytime. It's not as fast but it's very fast and doesn't have all the problems the other has.