Triggers using PL/pgSQL

Hello,<br /><br />I am interested in developing some triggers to keep track of records that are changed (possibly the
changesof one or more specific columns). In addition to keeping the new values, I also need to keep the old values (may
beon a separate table).  <br /><br />Though I  have done similar things in other RDBMs using SQL, I find doing this in
Postgres,a little bit complicated - may be because it needs to be done through a separate procedural language and
througha separate function. The Postgres documentation also didn't provide much help ( the examples in C). I was mainly
lookingfor example showing how to refer 'OLD' and 'NEW' rows using PL/pgSQL.<br /><br />Can someone please direct me to
somesuch examples?<br /><br />Thanks and regards,<br />-Thusitha<br />