Apple's Mac Pro Audio Update 1.0 for early 2009 Mac Pro models comes only with terse release notes, stating that the update "reduces processor utilization during audio activities such as playing or recording music." More information regarding installation steps is available on Apple's Web site. The update is available via Software Update and the Apple Support Downloads page. (Free, 1.64 MB)
Fun Way to Send Attachments in Mail
If you're working in a file that you want to attach to a message in Apple Mail, you can transfer the file to Mail easily: From the title bar of the file's window, drag the little proxy icon to Mail's icon on the Dock. Your Mac will make Mail the active application and open a new outgoing message, with the file attached.
(If your icon won't drag, the file probably isn't saved.)