To get Supremacy 1914 working you'll need a fairly current version of Java. For older systems Java updates have stopped. At the time of writing this if you have Mac OSX 10.7 or higher you can update the Java version to 7. Apple supplies their own version of Java, so there is no need to go to java.com.
Click the apple button, then go to software update.
From there you can select the java update and install it.
If you got powerpc Mac, then you could attempt to install Linux/BSD in a single or dual boot configuration. Depending on hard drive space you could run two operating systems.
Ubuntu, OpenSuSe, MintPPC, Debian and so forth offer powerpc based distributions.
If you run Mac OSX 10.6.8 or under you could switch to Linux/BSD if you want, because your not getting anymore Java updates from Apple.
Intel based Macs must have a distribution that is Intel x86 (32 bit) or x86_64 (64bit)(AMD64). Powerpc based distributions will not work.
G5 Powerpc's can run powerpc64 (64bit)