As both these tasks are critical to database performance over the long term, starting in PostgreSQL 8.1, there is an autovacuum daemon available that will run in the background to handle these tasks for you. Its action is triggered by the number of changes to the database exceeding a threshold it calculates based on the existing table size.
The parameter for autovacuum is turned on by default in PostgreSQL 8.3, and the default settings are generally aggressive enough to work out of the box for smaller database, with little manual tuning. Generally, you just need to be careful that the amount of data in the free space map doesn't exceed max_fsm_pages, and even that requirement is automated away from being a concern as of 8.4.
