how do setup internet on OS X 10.2.3

Internet on that operating system and Mac is fairly limited:

1. No current Java (needs Intel Mac)

2. No Silverlight nor Netflix (needs Intel Mac)

3. No current Adobe Flash (an old version of TenfourFox or Wacom Mozilla may work better than other browsers). See browser versions on my FAQ*:

http://www.macmaps.com/browser.html

Also note, Apple menu -> System Preferences -> Network will let you connect via ethernet to high speed internet, but there is no support for WPA2 encrypted WiFi. That would have to come from an ethernet WiFi bridge that supports 802.11g or better.

No USB 2 support exists on Macs until Mac OS X 10.2.8. And for the PowerMac G4 tower there is only USB 1.1 unless you add a PCI card that supports USB 2. There is also only Firewire and internal hard drive booting. Most PowerMac G4s can be upgraded at least to 10.4.11 for some better internet support, though finding those discs can be hard. For more on upgrading see my user tip:

http://discussions.apple.com/docs/DOC-2541

You'll get a slightly more current Java and Flash with 10.4, and even more improved with 10.5, though 10.5 gets rid of Classic support.

At least with e-mails you can get both IMAP and POP3 e-mail depending on your needs.

Just don't expect to be able to use much youtube. The sad thing is, even a G3/233 was able to use 320x240 video with Quicktime Sorenson, yet the internet vendors ignored those capabilities and focussed on Intel Mac and better capabilities.

To respond to your signature, you may be interested in the following:

As for your iMac's lack of HDMI audio, there are a couple reasons for that, either the iMac is too old, or the adapter is not good. The age where Apple adapters support audio is on this tip:

About Mini DisplayPort to HDMI adapters - Apple Support

And this tip explains alternative adapters towards the end:

Can AppleTV make my TV a wireless display of my Mac?

* Links to my pages may give me compensation.