You can check some details via website. Just open the main Islamabad Excise website, go to vehicle information detail. Enter English Characters in first box and numeric characters in second box, and you can find the details (if available).
I checked mine for 3 vehicles, and they are there, exactly as they are / were.
As of now, any one can check details of Islamabad registered cars through website; you just need to know the registration no.