Do a Google search (
www.google.com) and
search on "palmapp.dot". Look for the third "hit"
from the top titled "Summary of Files Installed
by Palm Desktop 3". Review the details.
Essentially, palmapp.dot is part of an Office
suite emulation package designed for Palm
and Handspring devices. It supported Word
and Palmapp.xls supported Excel.
It seems that at some point you, or a previous owner
of your handheld, gave Palm Office emulation a try.
When they deleted the software, palmapp.dot was
not removed.
It's obvious that it's been on your unit for a while.
If it's not hurting anything, why not leave it alone?