I'll join this thread because I'm having similar problems.
- bog standard cheap Labtech headset works fine on XP on a Dell laptop.
- same headset plugged into a new PC with Windows 7 acts as if the mic needs a preamp. I need mic volume 100% and boost +20dB to get reasonable input levels using Windows 7 Sound Recorder. I cannot make Skype work at all - need +30bD boost to pass Skype's Call test, but noise is terrible and called party can't hear me if I try a real call.
Sound card is Realtek High Definition Audio and
driver is up to date.