'Hot' backup of PostgreSQL dbases

Using PostgreSQL 8.3.7, I'd like to make a 'hot' backup of my dbases.

I've been using "pg_dumpall -c -o" for a while, but I realize that this is

no good. After all, for a restore, the PostgreSQL server needs to be up!

And what happens if the dbases crash/become corrupted (say, after a

power-outage), and PostgreSQL won't start up any more? In MySQL, this was

easy. In a Perl script I did something like: "FLUSH TABLES WITH READ

LOCK", and then I proceeded to tar the entire dbases directory (so I could

untar, without the MySQL server needing to be up).

Can something similiar be done in PostgreSQL, *without* bringing down the

server in its entirety?

Thanks,

- Mark