where is comments located?

Howdy:

Running PostgreSQL 7.2.1 on RedHat Linux 7.2.

What table is 'comments' referred to? For instance,
if you should put a comment to your table and / or
columns, where can I query the comments for
said table only?

What I want to do, since I don't seem to be able to drop tables
based on a creation time / data parameter, is find out if a table
has a comment on it; if not, drop that table.

I imagine that the comments would be listed in some
pg_* table name, but I am going over the documentation
for system catalogs and I don't see a reference for
that.

Any suggestions?

Thanks!

-X