I have a compaq laptop, running windows XP classic. Oker headphones... works on a friends Mac, not on my PC. I can hear sound through the speakers and headphones at the same time, but the microphone isnt working at all.
 
I a bit of a hardware dunce. Any suggestions?
 
I'm in Bangkok and want to Skype home to Bonnie Scotland.....

Double-check the basics: is the microphone plugged into the microphone jack?
If so, you may need to uncheck "muting" for the microphone in the Windows sound "mixer".  You should be able to get at that by selecting "advanced" mode   after you double-click on the little speaker icon in your system tray at the bottom right, IIRC.

If you haven't already, check out the free Sightspeed software.