Where to start for performance problem?

I've scanned some of the archives and have learned a lot about different performance tuning practices. I will be looking into using many of these ideas but I'm not sure they address the issue I am currently experiencing.

First, I'm a total newb with postgresql. Like many before me, I have inherited many responsibilities outside of my original job description due to layoffs. I am now the sole developer/support for a software product. *sigh* This product uses postgresql. I am familiar with the basics of sql and have worked on the database and code for the software but by no means am I proficient with postgresql.

The archives of this list provides many ideas for improving performance, but the problem we are having is gradually degrading performance ending in postgres shutting down. So it's not a matter of optimizing a complex query to take 5 seconds instead of 60 seconds. From what I can tell we are using the VACUUM command on a schedule but it doesn't seem to prevent the database from becoming "congested" as we refer to it. :] Anyway, the only way I know to "fix" the problem is to export (pg_dump) the db, drop the database, recreate the database and import the dump. This seems to return performance back to normal but obviously isn't a very good "solution". The slowdown and subsequent crash can take as little as 1 week for databases with a lot of data or go as long as a few weeks to a month for smaller data sets.

I don't really know where to start looking for a solution. Any advice on where to start, understanding that I am a newb, would be greatly appreciated. Thank you.

Nid