Hi medici712:
From
Everymac.com's Power Macintosh G3 FAQ:
"
Can an ISDN, Cable, or ADSL connection be used with the Power Macintosh G3?
Yes. Along with every other Mac that has 10/100Base-T Ethernet pre-installed, both the original and the Blue and White Power Macintosh G3 series is designed to accommodate ISDN, Cable, ADSL, and other high-speed connections that plug into the Ethernet port."
Hope that helps!