You should be able too in the game client.
If not open up your eqclient.ini file and find the [VideoMode] area and edit away.
Mine looks like:
Code:
[VideoMode]
BitsPerPixel=32
WindowedWidth=1680
WindowedHeight=1050
Width=1680
Height=1050
FullscreenBitsPerPixel=32
FullscreenRefreshRate=0
Runs pretty on my 22"