Q: DOES a powermac G4 require special monitor cables or other plugs different from most desktops?

To the best of my knowledge, every G4 Power Mac shipped with at least a VGA connector. That was the standard at the time.

Power Mac G4: Display Compatibility...

http://support.apple.com/kb/HT1825

Keep in mind that a Power Mac G4 is a very old computer, in terms of its dated hardware and inherent limitations.  If you want to use it for internet browsing, I'd recommend looking for something newer.  If you only need it for word processing, accounting, etc., it would be more than adequate for that type of usage.  I would suggest that you not pay too much for it, especially if it's running a pre-OS X version of the Mac OS.

Make sure the PRAM battery is current.  

Try to get the original discs, as they are hard to find without the machine.

If possible buy it with a current system such as 10.4.  All G4s can at least get up to 10.4.11.

Some of the more current ones can get up to 10.5.8, but not all will support Mac OS 9 booting under 10.5:

https://discussions.apple.com/docs/DOC-1757