Why doesn't an extended microphone help with the background noise on Skype?

It could easily be electrical noise from the internal fan or other electronic components in or around the laptop. Unfortunately the FCC requires certain audio components to allow frequency interference for reasons I’m not going to bore you with. If you’re using Windows 7 there’s a feature in the sound settings (under recording) where you can have it try to compensate for ambient noises… which might help a bit. Other than that you might want to test out some other mic brands to see if you still have the same problem. Take your laptop with you while shopping around so you can actually test what works/doesn’t work.