From Conrad...

In Windows, go to...

C:
Documents and settings
Your profile name
Application data
Skype
shared.xml
Use any text editor like Word Pad or Word to open and edit this file, as shared.xml is a real text file
Nearly at the end you will find

<UIVersion>0/1.4.0.84</UIVersion>
<VoiceEng>
<AGC>0</AGC> <-------------------------------------- add this line
<MicVolume>xxx</MicVolume>
</VoiceEng>
</Lib>
<UI>

Edit this and SAVE
Don’t forget to shutdown Skype before doing this.
Skype will not allow any changes while running!
You must set the signal volume now manually for best quality