How to get both audio devices working together?

So i have a headset i use for gaming and it has a headphone and a mic jack, at the moment i have it set up so i can hear my xbox 360 and my computer sound at the same time with my xbox sound coming from the line in jack. When i try to use my mic however it uses my xbox sound instead i can get my mic to work if i unplug the line in jack coming from my xbox but then i cant hear my xbox. So i was wondering if there is anyway i could use both at the same time.
Any help would be apprieciated.

What card does your PC have? Try going into the drivers or in windows control panel, and set recording default to mic and not line in. Also, unmute your line-in and mic and test at the same time. See what happens. And again, what card does the PC have??