Simplest road to automating actions?

[devinl]

I have a folder containing JPGs of page scans. Each page is "4-up," that is, has an image in each of the four quarters of the page. I'd like to automate a process of GIMP reading in each file in the folder, centering the image on an 8-1/2" x 11" canvas (in case the original scan wasn't exactly this size), then parting out each of the four quarters into separate files (ideally named as the original file, but with -1, -2, -3 and -4 as suffixes).

Given that I've never used scripting or other automation in GIMP, can anyone suggest the simplest route, that requires the least amount of education on my part?