Obtaining the exact size of the database.

Hi All,
I am using Postgres 8.1.9 for my application. My application also has
a clean up module which cleans up specified percentage of total database
size at regular intervals. Now the problem is I use *pg_database_size* to
obtain the size of the database. After deleting the records, we run *Vacuum
Analyze* to reorder the indexes. The problem here is even though some
records are cleared, it still shows the original DB Size. Is there any way
to find out the actual DB Size or it would be more useful, if I can get the
size of each table.
I can't run *Vacuum Full* because the application should be run 24*7
without downtime.

Can someone please help me in solving this.

Please let me know if you need any clarifications.

Thank you,
Venu.