I doubt that problem is caused by the sound driver. Most likely a bug between the application and it's settings or the way it communicates with the software. I seriously doubt you will find a sound driver labeled:
"Use this driver if you don't have mic sound while chatting in yahoo messenger 10.0.1"
The only Advent 5401 support I'm aware of is located here:
http://www.uktsupport.co.uk/advent/laptop/5401.htm