GIMP Plugin Registry

Hi,

I have a lot of images in certain format, e.g. grayscale TIFF at 600dpi.
I would like to script processing of the bulk with GIMP
to convert them to lower resolutions (300dpi, 100dpi, etc.)
as well as black-and-white as for sure I am not keen to do
it manually one-by-one.

I did a quick search in the existing plug-ins and the manual and
was not very lucky so far; any pointers in the right direction
are appreciated if available. I could probably script the plugin
myself quickly if I were intimately familiar with the related
API of GIMP in either Scheme or Perl, but it'd take me some time
to figure out, but I need my conversion sooner than that.

Thanks.