If ADC is the only connection available on your display, then you would need a DVI>ADC adapter. (MDP to DVI is included in the box of a new mac mini, so that would be MDP>DVI adapter to DVI>ADC adapter to Display)
This is
- not available anymore in stores. Maybe 2nd hand ?
- new price was 99$
- not elegant: the brick provides the power for your display.
(Your G4 video card with ADC output, provides power to your screen, through the ADC cable.)
It is possible you run into problems, two adapters to convert video signal is not ideal...
Conclusion:
If I were you, I'd buy a new display (or second hand) with HDMI or DVI input.
LCD displays don't cost a fortune anymore, and provide decent quality for the average user.
LED displays are more expensive, buy this only if you really know why.
HDMI cable: a cheaper cable will do. A cable of 60$ doesn't give you better quality then a 15$ cable. In the digital domain you have either a perfect signal or no signal at all. If you want I can explain more.
good luck