Have you done the usual..?
Right-click somewhere on the desktop, choose Properties, Settings tab, Advanced button, Monitor tab, CLEAR the "Hide modes that this monitor cannot display" checkbox, go to the Adapter tab, click on the List All Modes button. This should show all sorts of silly sizes and refresh rates. :-)
Monitor capabilities that will show in standard selector lists can be set by editing the .inf files... if you know what it is called... and where it is...
