device full ---> postgres will not start

Hello:

It looks like I got caught sleeping.

I am running Postgresql 7.2 under Red Hat 7.3.
Postgresql failed today. When I tried to restart it, I got a message
stating that the device is full.
I used df to confirm that /var where postgres reside is full. /var is on a
4 Gig device.
Postgresql is the only application on this machine.

Please note, the backup of the database from the prior day, is 45 Meg
zipped.
I do not know how the database could be soaking up a 4 Gig device.

Questions:

How can I recover from this situation?

If postgres will not start how can I restore the database from the prior
day?

When I run a backup does postgres truncate its logs?

please keep it simple, I have about 1 hours admin experience with postgres.

thanks in advance.

kd