You can only run LW 5 if you can install Java 1.6 (6). And Mac's Java 6 is only 64-bit compatible so only the newest intel computers are able to use that java since they are 64-bit. So depends upon your computer.
If you can tell me the brand model, I might be able to find out if it is compatible.
Mactracker - get info on any Mac keeps track of all the apple computer models.