Creating numeric type by hand?

Hi all:

I have Postgres 6.5.3 installed on Linux... well, sort of. The problem
is that the installation in question must be screwed up somewhere,
because I can't find the "numeric" type in it (while I can find it in
another clean 6.5.3 install), and now I need it for a project. My
question is: what do I have to do to create the type in question by
hand? I suppose that I have to connect to the "template1" database and
edit the pg_* tables... but which ones?
Of course, a possible solution would be to dump everything and
reinstall Postgres from scratch, but I can't even do a pg_dumpall in it;
it tells me:

Can not create pgdump_oid table. Explanation from backend: 'ERROR:
Relation 'pgdump_oid' already exists'.
pg_dump failed on [db_name], exiting

(If anybody can explain possible causes for this error, I'd be grateful
too).

Paulo Jan.
DDnet.