2 jacks in laptop and one in Headphones

[KD1316]

My new headphones have a dual jack but my PC has 2 ports so I can either listen to the sound or speak into the mic.
How do I get them both working at the same time... Please help!

(The headphone pin has 4 metal sections)

 

[alexoiu]

There are adapters like http://www.amazon.co.uk/StarTech-3-5mm-Headset-Splitter-Adapter-Black/dp/B0058DOWH6