General question about DBI/DBD

I've got a very big program that I wrote using Pg.pm, and now I'd like to
convert it to using DBD:Pg.  Can anybody give me any general tips on how
to do that?  Just convert all the $conn->exec to $DBH->do, or is it more
complicated than that?

Also, the big program does a whole bunch of
  $conn->exec("SELECT * FROM tablename WHERE indexed_column = '$key'");
and things like that.  Is there a way in DBD:Pg I can re-parse those
queries with "...indexed_column = :1" and then supply a different key each
time?  I remember when I used to write C programs that accessed Oracle
(about 8 years ago, so the details are hazy), that was a major performance
improvement.

--
Paul Tomblin <ptomblin@xcski.com>, not speaking for anybody
"I had to kill him -- he was starting to make sense."