Wajih is right but perhaps he has generalised the whole procedure. Let me give you a detailed road map.
For Islamabad Registration, first of all you need to prove that you are a temporary or permanent resident of Islamabad. Your NADRA ID card will help do that. But if that card contains address other than Islamabad, you need to get a 50 rupees judicial stamp paper for an affidavit from an owner of a house in Islamabad that he has rented out his house to you (he//she may be your relative to oblige you) or you need a certificate from your company that you work and live in Islamabad. This should be accompanied by 2 utility bills, gas, phone or electricity. Mobile or credit cards' bills not accepted.
Part II. You require a Form F and Form T-1 (if its an already registered car). The attachments with Form F would be 2 copies of Invoice and 1 copy of Sales Tax certificate. These should be attested by a grade 17 or above officer of tyhe government of Pakistan with his name & designation stamp/seal. Your Nadra ID card should also be verified by the same person.
Part III. You would require a Form 32-A (in triplicate) for depositing fee at SBP counter or at National Bank of Pakistan, F-8 or Melody branch. You will have to deposit 1.5% as advance tax, if the car is nor "invoiced" in your name and 1% registration fee of the value of the car. If the car is a used one, the Excise Inspector shall assess the value of the car and shall be binding on the applicant to accept. If the car is being transferred Rs. 1200 or Rs. 2000, as the case may be according to engine displacement also needs to be deposited.
Part IV. You would also need a Rs. 20 stamp paper, duly notarised by the oath commissioner declaring that the car that you intend to transfer or register in your name is not a stolen one & if subsequently found stolen, you shall be held responsible.
Part V. Get a file cover and a photocopy of all above documents because there is a fair chance of papers being misplaced. Excise ppl would require the file cover. Get an application typed in the name of ETO Islamabd requesting registration of the car and trhe documents that you have attached.
Approach the window for inspection of the car. For that take the car to F-8 near the IG office. Parking would be a great hassle. Squeeze in and "request' the inspector to verify the engine and chassis numbers.
Submit all documents to the dealing clerk and ask for a registeration number. If everything is in order, you shall get a chit and Reg. Number KD-678 type with the date three months ahead to collect the papers. Rs. 100 extra if you need a registeration book.
If you get the officials plates within a week, well and good, otherwise have your own plates made. Goto samad brothers @ aabpara. Rs. 280.
Get a photocopy of the chit and keep the original in glove case of the car at all times. This is your passport to be out of plice station.
When you get the book, go to your nearest post office for getting it registered there and depositing the road tax and advance income tax, adjustable in your yearly tax returns.
Also check if its within 15 days time of registeration. Otherwise approach the dealing clerk for extension in date by giving an application to the ETO Islamabad, requesting condonation of the delay.
I hope you will be able to manage the above easily NOW.