migration between databases and versions

I have been Red Hat linux 7.3 on my prod server. I have been running
postgres 7.2 on it.
I would like to upgrade it to the newest version of postgres.
1) Is there a version for redhat 7.3.
2) How stable is postgres 7.4 ?
I have another critical isssue.
My database has now changed.In our new release of the product we have
added few more columns to some of the tables in the database. But the
production does not have these fields. All the fields in the tables in
production are also in developement version. But there are some extra
fields in developement database that are not in production. There is a lot
of data already in the production database.
Now i need to add move the data from the old production database to new
one which has certain extra fields. Please let me know if it is possible
to do this migration, if yes how? using pg_dump?

Eg: Old database with data
has a Table named 'person' with fields A,B
New Database to be put under prodcution
also has an Table named 'person' with field A, B,C

If i do a pg_dump from old to new does it fill the A,B and leave C alone
or will it give an error given that C is not a null field.

Please help me

--Mohan