I usually press TAB to select directories on Windows, how do I ask it not consider internal svn folders (e.g. .svn)
You can’t; the filename completion key cycles through all files/directories, including hidden ones. There is no special provision for selecting only certain file/foldernames. You may be able to find a third-party command-prompt shell (eg 4NT, Console2) that has the ability, but I have not seen any that actually do.