Hi Sandy,
There are several ways to do all this.
You can create a web based form out of what you have, that will simply email all the info to you and you can then process it the same way you do now.
here are some samples:
https://secure.pon.net/referral/area/dslbusiness.htm
http://www.webperception.com/webpercept ... ignup.html
http://www.clipper.net/content/dsl_form.php
or,
You can create an online order system using that form and /or any other forms that you need.
In your cpanel ( as mentioned above ) is a billing system called "phpcoin" that may be enough for what you need.
otherwise, here are some links to free/open source software for this purpose:
http://www.freeside.biz/freeside/
http://www.jbilling.com/
just depends on what you want to do.
robert