Query About vacuum and pg_dump

Hi!!!!!

We have got "PostgreSQL 7.2.1 on i686-pc-linux-gnu, compiled by GCC
2.96 " running on Linux 7.3.
There are 2 databases , each of size 16 GB.

I have 2 queries regarding vacuum and pg_dump.

VACUUM :

We run "vacuum " for each of the table in the database on daily basis.
But it doesn't seem to reduce the disk space.
We also tried using "vacuum analyze". But no change was observed.

pg_dump:
we use pg_dump command to take the backup of the databases .
I would like to know, how will it affect if I run the pg_dump while the
tables are being used or when the transactions are being processed.

Thanks in advance and Waiting for your speedy reply.

--
Regards,
Pragati

Whatever you do will be insignificant, but it is very important that you do it.
-- Gandhi