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

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

The video system provided in the eMac models cannot be upgraded, but some can be "hacked" to support a non-mirrored external display.

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

Officially, Apple states that the eMac 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 original eMac models -- the eMac G4/700 and G4/800 -- 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 ATI Radeon graphics processors used in all subsequent eMac systems, 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 ATI, USB 2.0, and 2005 eMac models to support a second display in "extended desktop" mode.