pg_xlog and standby

hello everybody:

im trying to reconfigure a warm-standby server. the problem is that
for some reason, one day the standby server stopped recovering the
archives. this leaded to a full disk on that server, so i turned off
(commented) the archive_command on the main server.
i want to restart the procedure described in
http://www.postgresql.org/docs/8.1/interactive/backup-online.html#BACKUP-PITR-RECOVERY
but i dont know how to "safely clean" the main server $DATA/pg_xlog/
dir.
with "safely clean" i mean how do i know which archives can i delete
(or move somewhere) without disrupting the normal operation of the
server.

im using postgres 8.2.5 from source on debian etch.

thanks in advance!

--
Roberto Scattini
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