Full screen mode

[Chrushev]

or you can use the installer in my signature and pick the option that says "Fullscreen/Windowed" and pick the settings you want.

or you can simply edit eqclient.ini and set

[VideoMode]
Width=<your resolution>
Height=<your resolution>
WidthWindowed=<your resolution>
HeightWindowed=<your resolution>
WindowedWidth=<your resolution>
WindowedHeight=<your resolution>