To connect your Feedburner Email Subscriptions to the (in)SPYR Subscribe widget you’ll simply want to login to your Feedburner account.
Click Publicize and then Email Subscriptions.
Copy the hidden fields from the section show below.
And enter the following Form Action, Email Textbox Name and replace Hidden Fields with those that you copied from your Feedburner.
Form Action:
http://feedburner.google.com/fb/a/mailverify
Email Textbox Name:
email
Hidden Fields:
<input type="hidden" value="FEEDBURNERURI" name="uri"/>
<input type="hidden" name="loc" value="en_US"/>