New to Mac - need network help

Here's my situation:
I'm a long-time PC user who just inherited an old eMac, and was going to set it up for my toddler son, but I can't for the life of me get this thing connected to my network (and I feel like a fool)!
eMac Specs:

• eMac ver.2.1 circa 2002
• 700MHz power PC G4 | 384 MB RAM
• OS X 10.2 (6C115) | should mention this is a clean install from original discs
• no airport card

Network setup:

• ISP - Cox Communications
• D-Link DIR655 wireless router
• 4 PCs wirelessly connected/2 wired
• eMac connected via on-board ethernet port
• connectivity and Cat5 cable checked/functioning

I've tried:

• Network Setup Assistant
• manual config per instructions in eMac manual
• everything that's ever worked in my experience
• pulling out my hair one fist-full at a time

All of the info/directions/guides I could find online have slightly different looking windows and options for setup than I see - can't update OS X - couldn't find stand-alone update (only upgrades)........anyway, I'm sure I'm doing something stupid or not doing something simple, but I'd greatly appreciate any directions or advice or links you might have. This is driving me nuts - my folks had great luck with this old machine and it was online using the same ISP for years, and I'm sure it'd be great for my little man.