What is the .pst file size limitations?

I would like to know what the file size limitations are for Outlook 2000. I have a lot of customers who run into issues with Outlook because the use it for a data repository. I end up having to create a .pst on their local hard drive, give them a disclaimer of why it is not good to have the .pst local, and they continue to add emails, etc. to the .pst. We have customers who have .pst file in the 2-3 GB range. Does anyone have a link to MS or other reference? I would love to have some hardfacts to give the customers as to why they must delete old messeages (or archive).