You cannot embed forms on Pressero pages. However, you do have two options for adding a Constant Contact sign up to your site:
1) You can get a sign up link from Constant Contact. You can add this link to your website. Here is a link to instructions for doing this:http://support2.constantcontact.com/articles/FAQ/2514
2) You can add an iframe to a page with the form. Here is an example of what this would look like:http://onlineprinting4retail.v4.pressero.com/page/signup
If you are using a standard skin, this can be added in any place where
you have the text editor in the Pressero admin area - such as a custom page. It can also
be added via a custom skin.
To set this up:
1) You need to get a code snippet for the form from Constant Contact. Here is a link to those instructions:http://support2.constantcontact.com/articles/FAQ/1538
2) Download this file
and open it in notepad.
3) Paste your Constant Contact code snippet from step 1 where indicated in the .html file from step 2. Save.
4) Upload this file to your website via the File Manager in the Pressero admin area.
5) Add the following code into the html tab of your text editor in the Pressero admin area:
<iframe src="http://orderingplatform.com/files/Subscribers/448cc937-d8f9-4cf0-96f1-01e91ed0ad9c/webfiles/cc.html" height="100%" width="100%"></iframe>
You will need to replace the path in this example with the path to your .html file uploaded in step 4. Adjust the height and width of the iframe as needed. Save.
Please see this related article: http://support.aleyant.com/KB/a161/is-there-a-way-to-create-a-newsletter-sign-up-on-my-site.aspx