Can I run two Postgres sessions at the same time?

I have a small business I am helping with their Postgresql server. They
may need to move one of two databases onto a seperate disk system. They
don't want another physical server. Can I run two postmasters pointing
to different disk areas
(i.e. /usr/local/db1/data , /usr/local/db2/data)? Can they be on the
same port?

Thanks.

Steve Poe