Richard's suggestion is good.
I have W2000 and the microphone failed when using the testcall facility, which was misleading.
However found it works ok when making a normal call. Having a wireless router helps, as I could test to 'er indoor's' laptop in the same room.
I put this down to having an older pc and os.
In case you are unaware, when making a call, there are some sound adjustments available on Skype.
Good Luck - Keep us posted.