@alayham.... Dude I also get this problem and i search alot of solutions for it but at the end i decide to Convert my Original N900 Headphones into Normal headphone. Now my headphones works on my N900 n also on my Laptop. But MIC is not working. Here is the DIY Link

http://talk.maemo.org/showthread.php?t=66111

Hope so it'll help you.