I try to use skype on aspire 1 but fail the call test: I cannot

First: Check if the device is installed and working properly - My Computer-(right click)-Manage-Device Manager - be sure there is nothing wrong in "Sound, video and Game Controllers" section.
If there is something wrong, you will see it immediately, then fix it.
If in that section all is OK, then
1) go to Acer FTP site and get Realtek driver there (ftp://ftp.work.acer-euro.com/netbook/aspire_one_150/driver/Audio_Realtek_v.5.10.0.5772.zip).
2) Uninstall running Realtek driver using Control Panel and reboot.
3) When XP after reboot will ask for driver installation, just cancel this and install Realtek driver downloaded.
4) Check with Skype your voice recording and enjoy.
All this is valid if you do not have your microphone physically broken. Tested by myself - I had the same situation.