Well for a start that 15 ohm resistor is way too low, you will draw too much current out of the arduino pin and damage it. So you need to either up it to about 100 ohms or use a transistor to switch it.
Then you need to find out at what speed the Ir is being modulated at and change the PWM timers to that. Then you need to flash that modulated ir on an off in the right code sequence.
There is a good Lady Ada tutorial on this sort of thing, but it is too long to give all the detailes in a post reply.
I have noticed that your hardware diagram is from an instructables project. These are usually very very poor when it comes to electronic hardware, my advice would be never to use them with out asking a grown up first.