Can I safely kill a VACUUM ANALYZE with pg_cancel_backend 8.3

HI,
I have a vacuum process that has been running on a table for the past 20 days.
The server is postgres 8.3 on ubuntu linux.

Can I safely kill the vacuum with:
select pg_cancel_backend(26433)

Some stats
The table sees ~5million and not more than ~10million updates month

$ ps aux | grep 26433
postgres 26433 0.0 1.5 35468848 2012212 ? Ss Apr08 26:00 postgres: autovacuum worker process foo

foo=# select procpid, now() - query_start, query_start, current_query from pg_stat_activity where current_query != '<IDLE>'order by 1 desc;
procpid | ?column? | query_start | current_query
---------+-------------------------+-------------------------------+---------------------------------------------------------------------------------------------------------------------------------------
26433 | 20 days 20:11:32.386244 | 2010-04-08 14:19:59.298784-07 | autovacuum: VACUUM ANALYZE public.message

Thanks,
Jason