Backup of large objects

Hi,
I am novice to postgresql and I have some doubts about it .
1) How to backup Large objects, because pg_dump will not backup the large
objects. Can anybody help with some examples.
2)How big is the database that postgresql can support?
3)How to change the size and datatype of   a column in a table.
4) Up to which point can  the data be  restored? Is it upto the point of
backup taken or upto the point of system crash?
Thanks,
chava
_________________________________________________________________
Get your FREE download of MSN Explorer at http://explorer.msn.com