The stock cards that come with the G4s usually have 1 DVI and a VGA port.
No, this only happened in the first G4 models (Yikes & Sawtooth), the more usually video card connectors are ADC and DVI.
I'm in a predicament. I use video cards with 2x DVI connectors on them so I can have a dual monitor setup.
I use to have dual monitors setup too.
Just for the record, with two monitors the video card performance usually decrease in a half.
And as a curiosity, you can connect a Mac Os 9 video card with DVI output to a HDMI monitor with a cheap DVI to HDMI adapter, but without audio of course.