serial type question

I have a table that I want to add a serial type column. Is there a way
to add it or do I have to create a new table and insert into it. I have
experimented with:

insert into newdb (name) select name from olddb order by jobno;

however, pg does not allow the 'order by' during an insert/select

I am on version 7.0.3

Maybe I don't need to do this. What I am trying to accomplish is to
have PG create job numbers. Today, I only have 2 workstations that
push jobs into the server and PG tracks the job number. However, I
have been informed that in the next 6-8 months the number of job
creation workstations will grow to 8 - 10.

I would like to migrate to a job number created when the insert is
done.

Thanks for your help.

Ted Petrosky