pg_toast

I'm a newb to Postgres, and need some assistance with pg_toast. I'm running PostgreSQL 8.3, and am having an issue with one of my pg_toast tables growing at the rate of 1 GB per day. Can someone offer me some insight on

a) the functionality of the  pg_toast_* tables?

b) how can I clear them out (or should I - including the reason if I should not)?

Reindexing produced no reduction in size of the table in question, and a VACUUM ANALYZE VERBOSE pg_toast_293523 produced the message:

    skipping "pg_toast_293523" --- cannot vacuum indexes, views, or special system tables.

I'm assuming truncating a pg_toast table would be a bad thing...

Any help would be appreciated. Many thanks.

- Mike