mailing in batches

I want to set up a script that sends a bunch of emails - pauses - and resumes until all messages are sent. The way this will happen is that a person will create the newsletter, check it, and then press the "Send" button which will start the process of sending the mail in bunches. How do I get a script to run in the background? I am only familiar with processing script within an html page that is returned to a client. Will a script like this keep running even if a browser window is closed? Also is there any examples of this kind of app? Regards, Matthew Delmarter Web Developer AdplusOnline.com Ltd www.adplusonline.com Phone: 06 8357684 Cell: 025 2303630