I am running centOS Linux 4.3

I can access the default page using 192.168.2.3:9999 on my browser from my network computer

However, even with port forwarding an firewalls disabled, I am not able to use my public ip address 74.xx.xx.xx:9999, it says page cannot be displayed. Can someone give me some advice on this?

Well, when you try and access it from 74.x.x.x are you still in your internal network when you do that? You'll probably have to be outside your network before you can access that way. If you can't test that easily yourself you could call a friend and see if they can access it. or you could email me with the ip address and I could test it for you. Click on my username and there is a link for email if you would like to try that way. (if you trust me to do that)

You are positive the port forwarding is setup correctly (no typos?)?