Questions On Tablespace

Hi Everyone,

I have questions regarding tablespaces, What happens when the disk on
which my tablespace is in fills up?
How do I expand my tablespace, in oracle there is a concept of
datafiles? In postgresql I specify a directory instead of a single
file...

For example I have two tables and they both use a single tablespace.
After some time the tablespace fills up. How do I point one table to
use a new tablespace?
Or is there a way in which I can get my tablespace to increase size by
using another disk for this purpose?
What's the best approach to this situation?

Thanks A Lot
Carlo