The product and subdomain fields must be customized.

Product should be one of basecamp, backpack, campfire, or highrise.
Subdomain should be the subdomain portion of your account's URL.

Example for a Basecamp account located at http://acme.basecamphq.com:

<input name="product" value="basecamp" type="hidden" />
<input name="subdomain" value="acme" type="hidden" />
