Does enabling message journaling in Exchange 2000 Server affect system performance?

Yes, but the impact will likely be minor. When you enable message journaling by selecting the Archive all messages sent or received by mailboxes on this store check box on the General tab of a database's Properties dialog box, you're telling Exchange 2000 to make a copy of all messages in the specified database and store them in a mailbox or public folder. Making and storing these copies adds additional overhead; however, unless you have extremely busy servers, the additional overhead shouldn't cause a problem. The bigger concerns surrounding message journaling are how you're going to keep up with the volume of messages generated and whether you need to back up, archive, or otherwise retain the messages for any length of time.