invalid page header in block 52979 of relation "pg_attribute"

This morning I got bitten by the "SELECT INTO" / "CREATE TABLE AS"
from tables without OIDs bug in 7.4.1.

Postmaster killed all the backends and restarted - pg was down for 2
seconds.

This happened two times within a few minute period.

Now I am getting 'invalid page header in block 52979 of relation
"pg_attribute"' errors in the postgresql log file. I cannot reindex
or view the table at all even as user postgres.

I have not tried a manual restart of PG.

Although hardware could be an issue I tend to doubt it. This server
passed an extensive memory test before going into service and I see
no occurrences of this error prior to the crash but several since
then.

This is a 24x7x365 system. I do have a dump from this morning (I do
two per day) but I would prefer to fix the problem with no downtime
or data loss.

What serious problem is this likely to cause/be causing? What are my
options for fixing it?

Naturally, quick replies are appreciated - this is making me very
nervous.

Cheers,
Steve