Opening cursor files in a graphics editor?

The cursor files uses X11 cursor type of files:

$ file /usr/share/icons/DMZ-White/cursors/hand2
/usr/share/icons/DMZ-White/cursors/hand2: X11 cursor

GIMP plugin

You need a plugin to edit cursors files with GIMP called "X11 Mouse Cursor (XMC) plug-in" which you can find here.

The X tool

You can also create your own PNG images and transform them to cursors files using "Xcursorgen" which can be found in the x11-apps package.

Third party

Gursor Maker is a front end for xcursorgen.

References:

• http://gimpchat.com/viewtopic.php?f=23&t=2201
• http://mailman.cs.huji.ac.il/pipermail/linux-il/2009-April/001196.html
• http://www.ehow.co.uk/how_7486801_make-own-x11-cursors.html

Xcursor Viewer can be used for preview cursor. It hasn't any editing features. Only viewing.