Unfortunately, this is (still) not possible.
I plan to try to add some sort of "importer" in future, but due to current product design I am not even sure is this absolutely possible. Currently there are too many restrictions in the template processor and it is complicated task even for me to add new template.
En brief: there is no difference in the Shaker itself. The only difference is in the template license.
In the free version all my templates come with "attribution license" which means that you must keep the credits at the bottom (the "design by wonderwebware.com" link). Additionaly, some of the templates are licensed for noncommercial use only.
The "Pro" version means that you get these templates with different license and you are free to remove the credits link and to use all the templates for commercial purposes.
Apart of this, there are no other serious differences between the freeware and professional version.
You don't need to buy unless you want to remove the link to my site from the generated template.
However, if you decide to get the pro version, you will get one year free upgrades (which means you'll get all new templates free).
Please, download the free version first. Test it. See if the tool worth its price. In case you can live with the license restrictions of the free version (=the credits link) - just use it. The main reason I built this tool is to get some more popularity for my site and that's why I ask for that link in the free version. And if you really need the "Pro" license - just click the "remove credits" button inside the program itself to go to the purchase page.
If you already tested the free version and want to purchase professional license, visit this page: http://wonderwebware.com/templateshakerpro/
The reason for this is, usually, in some antivirus/firewall software installed on your computer.
Please, check also your internet connection.
Finally, try to open wonderwebware.com - if it is not available, then there are too many downloads and the server is temporary down :-) :-) :-)