Transfer blogs from old wordpress to new installation?

I’ve never actually used wordpress.com, but it is supposed to have the same Export capability that your own WordPress installation has. On the (admin) Dashboard, look in the left sidebar under Tools. And you’ll see Import and Export.

As the instructions say when you Export:

When you click the button below WordPress will create an XML file for you to save to your computer.

This format, which we call WordPress eXtended RSS or WXR, will contain your posts, pages, comments, custom fields, categories, and tags.

Once you’ve saved the download file, you can use the Import function on another WordPress blog to import this blog.

Sounds like you are on your own to setup your Theme and Widgets again.