remote synchronisation

Hi,

new to the list, and relatively new to Postgres admin too but here's my
situation.

I have a website running on PHP/Postgres and I'd like to set up a secondary
box which can be used to fall back on should the primary die for some reason.
How would I go about ensuring the databases are kept current and synchronised
while the systems are both live, and how would I do a compare once the dead
box has come back up to allow me to load the missing data? can this be done
with any psql tools, or is it a case of getting jiggy with a ton of shell
scripting and PL/SQL?

incidentally.. the two boxes are remote to each other and both run apache and
postgres, serving the data to themselves.

thanks

a