How do I remove a folder from being source controlled with TortoiseSVN?
The easiest way is described here: http://tortoisesvn.net/unversion.html
That article is a bit wordy and some of the methods didn't work for me (like dragging the folder onto itself - Windows 7 wouldn't allow it)).
Here's what, in the article worked for me:
Simple: when you right-click on a working copy and choose "Export..." from the context menu, a folder browse dialog is shown where you can choose the folder where you want the working copy exported to. If you now select the very same path that your working copy is on as the target (i.e., you're exporting the working copy onto itself), TortoiseSVN will remove all .svn folders of that working copy.