This can be done with any image editor, but I recommend using IrfanView
When the screen is up you want to capture, press <Alt-PrintScreen>'
Open IrfanView
<Ctrl-V> ("Paste)
Crop what you want to keep
Decrease the color depth to 16 (in IrfanView, Image/Decrease..)
Save as a GIF file
Notes;
<Alt-PrintScreen> captures the current window (such as an
error dialogue) to the clipboard
<PrintScreen> captures the entire computer screen to the clipboard
