Set up your formmail by going to Comcast main page > click the little arrow next to Personal Web Pages > choose Web Page Building Blocks > Site features > formmail > template options. You may have to enable a form for your site if you haven't already done so. There are a fair amount of options, so template options may be good enough. If not....
I've discovered a way to use your own custom form, but you have to do the template first. Oddly enough, the formmail isn't set up to send the results by email as a default. There is a box to check for that in the template options, as well as a space to put a URL to a thankyou page for when the form is completed.
Create your template form including all of the fields you intend to use in your custom form. Publish it and view-source. Note the exact names that the template assigns to each of your form fields, ( ResEmail, ResName, A1, A2, etc. ). Hint: save the source code.
In your custom form, copy the form tag with the action and also the key. You can add a name and style to the form tag, but the action should not be changed. For each field, use the same exact name that was generated for the field in the template in your custom HTML form. I believe this works. This way you can customize by including the form within your own HTML page. You can add style or make the textarea bigger or color your submit and reset buttons, for example. The important thing is to actually create the template, then mirror the exact names for the fields.
I don't think you're supposed to do this, but this isn't custom CGI, it's just a custom HTML form. It will only work if you upload it to the same name that you created the template for.