Who is doing the submission on the HTML form? Do you have control over the format of the submission sent to you? Do you have control over the way you retrieve the submissions?
Our customers are doing the submissions. I don't have immediate control over the format but the 3rd party is willing to work with me to modify it. Same with the way its retrieved. Any ideas?
You could set up your web site to write the submissions to a file which you could then download and import (or, if in XML format, import directly).
Alternatively, you could use a plugin to get the e-mails into Filemaker and process them there. If you're running OS X, you can use Applescript to do the same.