When using Skype, MSN, etc voice chatting software, by default the sound is recorded softly and the opposite party has difficulty to listen clearly.
In Windows XP, we can enable Microphone Boost.
Go Control Panel -> Sounds and Audio Devices -> Audio tab -> [Volume] in Sound recording
Then, in Recording Control -> [Advance] -> tick [x]Microphone Boost
Enable this option will help the computer to boost up the voice. People will listen clearer.
In some of the Voice Chatting software such as Skype and VoipCheap, inside Tools -> Options -> Audio Settings.
There is a setting called "Let Skype adjust my audio settings". The feature will most likely disable the Microphone Boost which you have just set. So untick "Let Skype adjust my audio settings".