I use the a form to subscribe people to Constant Contact located here: http://www.kishwaukeecollege.edu/visitors_friends/departments/president_newsletter.php?page=331
We want to subscribe people to a specific list (giving them the option of choosing it is not necessary, it's a hidden field). However, since we have other lists in our account, if they're already subscribed to one of the other lists, it gives them an error of "You seem to be subscriber of our mailing list already."
Is there a way that this form can just check to see if they are a member of THAT SPECIFIC LIST instead of all of them?
It appears that you are using the Constant Contact sign up form generator. Our public version of the sign up form generator only allows contacts who are new to the account. We do this because it opens up a security hole by allowing anyone to update contacts where they know the email address.
However, we do have an add/update version of the sign up form generator. If you would like to use it, please send an email to the webservices team, and we can send it to you.
Is the update to the signup form generator take care of my problem with the contact already exisiting and cannot be added to the new list?
Yes it would fix this issue. It would allow contacts to update their information, which allows them to add themselves to additional lists.