bring the birth certificate and passport to the immigration dept in madinat khalifa, you'll have to sign some forms there (there are portacabins for typing there, just pay QR10), then go to building no. 2 for processing. we did it for only 10 mins. don't forget to bring your ATM for payment. we did pay QR580 riyals then, if i remember it right. :)

Panka's comment down is more complete. :))