I noticed that the scanlines script-fu was not present anymore, so I cooked up a new one. This one is completely self-contained. Has a few enhancements to it, making it easier to work with. Thanks to Federico Mena Quintero for his work on the original "Erase Every Other Row" script-fu which served as part of my guide.
The script-fu will install in "<Image>/Script-Fu/Enhance".
Tested to work in GIMP 2.4.5.