pg_class / missing tables

I'm trying to recover a database where some tables 'went missing'...

Short story: server was rebooted without being shut down properly, upon
bootup PostgreSQL (7.4.3) starts fine, but a couple of data tables
(along with their associated indexes and sequences) are gone. Other
tables are still there.

The missing tables aren't listed in \d or in the pg_class table, but
according to the sizes of the numbered files in
/var/lib/postgres/data/base/142772, the raw files must still be there.
What's interested is that if I try:

CREATE TABLE missing_table_name (foo int);

It does complain that the table already exists...

What's happening here?

Many thanks,

Wim