descending index

I'm creating a small database, for test puproses, in PostgreSQL
and after some unsuccesfull attempts to find the answer in the
pdf documentation i've turn to this newsgroup for help.

I have read (partialy) the reference guide from the official site
and stoped at topic create index. I can't find no mention about
creating descending indexes. Is there such a thing as descending
index in PostgreSQL or is it not needed?
If yes where can i find the propper documentation on how to create one?

I spent the last days rewriting some scripts that i used to create
a database in Firebird in order to be able to use them in PostgreSQL.
My final purpose is to write a small test application that can compare
results between Firebird and PostgreSQL.

Since Firebird and PostgreSQL are quite diferent in too many ways
i won't do some complicated database design and i try to use features
that are similar in both RDBMS. I know a lot of users are interested
in a comparison between these 2 database servers since they are both
Open Source and cost free so i decided to make this test application.
I would also appreciate some hints into creating a test sample in such
manner that it would be usefull for many users as a comparison for
speed, number of features, and so on ...

TIA.

--
Best regards,
Aplication Developer
Pirtea Calin Iancu
S.C. SoftScape S.R.L.
pcalin(at)rdsor(dot)ro