Re: PIA or other flights
Neera: Which US city will you be travelling from? If it's not New York then I think Ruiner's suggestion is quite good because there are flights from almost every major US city to London. And from there you have a nonstop British Airways flight to Islamabad.
If you are flying out of New York then I'd recommend to go for Emirates. Although it is expensive and you would have a short stop-over, I think it's worth it.