I receive hundreds of mails in Outlook’03 every day. How can I best manage with rules and local folders?

I receive hundreds of mails in Outlook’03 every day. They are from different projects that I manage and have different topics like finance, technical and management. If I put it in a folder based on Project, I do not have a view of all finance of management discussions and if I categorize accoring to Projects I face similar problems. Can anybody tell me if there is any best practice in storing mails and how can I best manage with rules and local folders?