OK, I finally figured out how to do a search on the entire archive.

Here's an example. First, hit the "Messages" link on the left, which
will display the current list of new messages.

In the upper right is a blank and a "Search Archives" button. In the
blank type in the search terms such as

OSS conversion

Then hit the Search Archive button. It will come back with a listing
of the most recent messages with the words OSS and conversion.

BUT how do you continue searching through the older messages ? The
answer is you hit the NEXT button at the bottom of the message
listing. The next batch of older messages is searched and the hits on
the search term(s) are displayed. Note that the blank space where you
type the search terms goes blank. It does not seem to matter. You
can just keep hitting the NEXT button and search the entire archive
very quickly !

Greg