how to "for each poly do X" ?

Hi All,

I'm working on a project processing a lot of landsat7 and other images
and tile-management is so far the hardest part I've tackled. I need to
break things into pieces, do some work on them, and then reassemble
them and stuff them somewhere else, largely unattended.

Under ArcInfo I'd use AML and cursors: basically for each polygon in
an index cover do X,Y and Z. I'm at a loss so far to how to do the
same thing with the open source tools I have. Namely fwtools, qgis and
ossim (all on windows). Where do I begin?  I imagine this to be common
scenario, how are/have other people handled it?

thanks in advance for your thoughts,

--
-matt