Incredimail is fun... as far as e-mail clients go. But Incredimail is the Fisher-Price of e-mail. It has backgrounds, emoticons, animation, and even sound. But it is not a professional e-mail client.
Incredimail has its own proprietary storage format, very similar to Outlook Express, with .imm and .imh extensions. On Windows Vista, you would the message store at c:\Users\<username>\AppData\Local\IM\. Incredimail does not support IMAP synchronization, so it is not possible to use an IMAP server as an intermediary for a migration of content to another e-mail client. So how to we migrate from Incredimail to Outlook 2007?