What type of video processor is provided by the iMac G4? Is it upgradable?

Information regarding the video processor is provided on the specs page for each iMac G4, but for your convenience, details regarding the type of video card and amount of video memory also are provided below:

The video provided by the iMac G4 models cannot be upgraded, but some can be "hacked" to support a non-mirrored external display.

Is it possible to upgrade the iMac G4 to support a second display in "extended desktop" mode?

Officially, Apple states that the iMac G4 models include a Mini VGA port that supports "video mirroring", with the contents of the internal display "duplicated" on an external display using a VGA display adapter (sold separately). It officially cannot be used in "extended desktop" or "screen spanning" mode, where the external display can be used as additional "work space". The video system is soldered to the motherboard and cannot be upgraded.

For the iMac G4/700 (FP), G4/800 (FP), and G4/800 - X Only (FP) this is correct, the NVIDIA GeForce2 MX graphics processor is only capable of "mirroring" the contents of the internal display on an external one. The graphics processors used in the other iMac G4 models, however, are capable of supporting an external display in "extended desktop" mode, Apple merely blocked this feature in firmware to protect sales of more expensive Macs.

Unofficially, while disclaiming that the author is not "responsible for any damage that you might do to your computer" there is a hack called Screen Spanning Doctor that makes it possible for the earlier 17-Inch models -- the iMac G4/800 17" (FP) and G4/1.0 17" (FP) -- as well as the "USB 2.0" models -- the iMac G4/1.0 15" FP (USB 2.0), G4/1.25 17" FP (USB 2.0), and G4/1.25 20" FP (USB 2.0) -- to support a second display in "extended desktop" mode.