Click Start > (if in XP, click Run) > Type in
regedit and press enter.
The Registry Editor will appear. Navigate to:
HKEY_CURRENT_USER\Software\Patchou\Messenger Plus! Live\DefaultSettings\
Right click > New > String Value. Name it
LogsDirectory and press enter to confirm.
Now double click it and for the value, enter the location of the folder you wish chat logs to be saved in.
Now when a new contacts sign in, their chat logs will be stored in this location by default.