You need to put the save file in the save folder for the game:
Vista/Windows 7: C:\Users\[username]\AppData\Roaming\LaxiusForce
XP: C:\Documents and Settings\[username]\Application Data\LaxiusForce
This assumes that your Operating System was installed on C:\, which is pretty typical.
You need to be able to view hidden folders to actually navigate to that location. On XP, this can be accomplished by clicking "Tools -> Folder Options -> 'View' Tab -> Show hidden files or folders". I assume the process is similar for other OS's.