unable to repair table: missing chunk number

Hi,

I'm having serious troubles trying to fix a corrupted table, and am
hoping the data is not gone. 

When I try to do any sort of SELECT, or COPY that accesses a part of the
table, I get:

ERROR:  missing chunk number 0 for toast value 12851102

I get this using pg_dump, the COPY command, or even if I just do a SELECT
when I access records with id's > 115,000 (out of around 140,000 records).

Is there any type of repair tool I can use to fix the table? Or am I
looking at off disk backups (problem is I don't know when the table went
bad).

A search on 'missing chunk number' produced no help. 

Any help on how I can get the data dumped to a file would be greatly
appreciated. I'm using Postgres 7.2.1 built from source on a
Linux 2.4.3-6smp #1 SMP Wed May 16 04:29:16 EDT 2001 i686 unknown
machine.

Cheers,

Alex