GUI doesn't work in OS10.0

I have a computer which came with OS 9 on it installed already, and a CD which I used to install OS 10.0 onto the computer. So now it has both OS9 and OS10 on it. Java on the OS10 works OK with most operations, but when I started making a GUI, it didn't go well at all. Things which should take about a second took several minutes to do. Problems like that.
So I wonder what I could do. Would installing a newer version of java help(I don't know which version is installed now)? Or would upgrading the OS to a new version of OS10 work? (Now, it's 10.0.4) Or do I need more RAM? Or maybe I need a new computer because right now it's a G3 computer?
Does anyone else have this problem?

Bringing OS X up to a modern version, and making sure that it has the latest Java version would be my first step.

10.0.4 is incredibly ancient.

Thanks for the advice. How do I find out which version of Java is installed on my MAC?

Open the Terminal application, and type "java -version" on the command line. That will cause the Java version to be displayed.