Error Handling problem for all of the GURU's outhere

I am trying to figure out the best to handle errors that i want to pass up to my client from the data layer of my application.

I am currently writing a DLL that connects to a database and is capable of populating and updating the database. I am using error handlers to deal with all possible errors that may occur. Including a list of my own errors that i enumerated and need to raise to the client.

I would also like to pass in an enumerated list of ADO errors that could take place and pass them back to the client as well.

Basically i'm looking for the best and easiest way to accomplish this. If more clarification is needed, please post and iwill glady provide it.

Thanks,
Trip85