There are two options from what I can see:
1. Recommended - Post via form in background.
This can work for almost any autoresponder that use form post method. Almost all do. We already have built in settings for you with all of the popular autoresponder services such as: ARP3 (AutoResponseplus), GetResponse, ProSender, AWeber and EmailAces, and 1Shoppingcart (Private Labels such as, mymarketingcart.com, webcontactpro.com, frontpagecart.com, marketerschoice.com, sellbettertoolbox.com, autocontactor.com, masterlisttools.com, autopilotriches.com, queencart.com, autowebbusiness.com , quicksales.com, 1automationwiz.com, and many more.) This will allow your members to signup thru a form in the background and is allowed and recommend by all autoresponder services becuse the IP address of the user comes from their personal computer.
2. Not Recommended but much easier- Subscribe by email. Sends email to from your website to your autoresponder with Members name and email. This works very simple and is very effective. But some autoresponder services refer to this as "scripting leads." The problem is that the email comes from your website's server and then the member's IP address is logged as your website's server IP address. All of your members will have the same IP address which is not there personal IP address. Also, if you are using your own server based autoresponder (like ARP3/AutoResponsePlus) some systems have to be set up in your control panel to accept leads via email.