Actually you could create a cursor from almost any icon file, by just creating an appropriate mask file. The PbmPlus filter pnmmask, makes this very easy.
To use these file under X Windows you would issue a command.
xsetroot -fg {color} -bg {color} -cursor {name}.xbm {name}_mask.xbm
Or if the Window Manager sets the cursors for various things you can set the cursor in its RC file.
See Also:
desc/bw-16 Small symbols which can easily become cursors
prog/bits-bw a number of other small symbols.