ERROR: invalid memory alloc request size, and others

We recently upgraded from 8.1.4 to 8.2.0 on Fedora Core 6, and are now
seeing a few rather ominous-looking messages.

The problem started with this one, during an update involving a rather
complex view:

ERROR: invalid memory alloc request size 1174405120

Then, when attempting to re-run the same update statement:

PANIC: cannot abort transaction 8682091, it was already committed

and then again:

PANIC: right sibling's left-link doesn't match

I ran reindex on the tables in question, which fixed the problem in the
short term and allowed the update to complete, but then I got the memory
allocation error and these overnight:

ERROR: invalid page header in block 3362 of relation
"index_clin_dal_staff_id"
ERROR: invalid page header in block 2325 of relation "index_clin_dal_batch"

I will gladly provide additional information to help track down and
hopefully solve this problem, but at this point I'm not sure what else
to include.

Any help would be much appreciated.

Thanks,
Jonathan