Actually we haven't setup a migrate option for the SSP plugin. We've been hoping to find someone like yourself who is doing the switch, not that many podcasters use the simple podcasting plugin so the opportunity hasn't come up until now.
If you do not mind contacting me at cio [at] rawvoice dot com, i can get the details about your site which would be helpful for making the transition to PowerPress easy.
Currently we know that the plugin uses a custom post type rather than a custom feed to provide a podcast feed. We have custom post type podcasting support in PowerPress, so this will be easy to deal with. The only part we need to develop is an import process, as the SSP plugin stores episode information in a proprietary field in the postmeta database table. Should be simple enough to migrate, we just need someone like yourself willing to help us.
By the way, PowerPress as a simplified mode, and an advanced mode, so if the reason for using the SSP plugin is because of the complicated settings, you can switch to Simple mode in PowerPress and only deal with the bare minimum settings needed to podcast.