How to deploy into a subfolder?

The default setup process worked well. But I'd like to have two different blogs on my web, living in different subfolders. (One in English, other in Slovak - I don't want to mix them in a single list.)
I haven't been able to make it run in the subfolder. I've tried the obvious googled solutions, but no luck so far.

The most output I got was:

`The page cannot be displayed because an internal server error has occurred.`

And I haven't been able to find any logs anywhere.

I've edited the Config.js to include the correct URL, path to DB, etc. I've tried fixing the web.config, but probably did more harm than good.

Any ideas?