So, I was developing in a folder outside dropxbox and I'd like to sync that folder to dropbox without copying into it. How am I supposed to do that on Windows?

mklink to the rescue:

mklink /D "C:\Users\Diego\Documents\Dropbox\DesiredFolder" "C:\Path\To\DesiredFolder"  

TaDa. A simple thing to do in linux with ln is also available under Windows.