1. Start by going to http://notepad-plus.sourceforge.net/
2. Click the Download link at the top.
3. Find the Download Notepad++ executable files link and click that.
4. From the list of files pick the highest version of the installer.exe.
5. Run the installer. The default settings are fine, so you can just OK, Next & Finish through the whole thing.

Now you can run Notepad++ and open your XML files to get your first taste.

1. Close Notepad++ and go back to the Download page on http://sourceforge.net/projects/npp-plugins/files/
2. Find the XMLTools plugin on the list of plugins at the bottom of the page and click its link.
3. From the list of files pick the highest version of the zip file that's not labeled with “source”.
4. Then click the External Libs link and download the ext_libs.zip file.
5. Extract the XMLTools zip file into your Notepad++\plugins directory.
6. Extract the ext_libs.zip file into your Notepad++ directory, not in the plugins directory.
7. Run Notepad++ and check that the Plugins > XML Tools menu is operational.
8. Make sure all your XML files have the following as their first line:

<?xml version="1.0"?>

Now you can use the syntax checking option from the XML Tools menu, or even enable automatic syntax checking to make sure your XML is at least well formed.

Or at last resort you can just replace your Notepad++ directory in program files with what's contained in this zip file :   Notepad++.zip (4.23 mb)

What is URN

Uniform Resource Name. A unique identifier that identifies an entity, but doesn't tell where it is located. A system can use a URN to look up an entity locally before trying to find it on the Web. It also allows the Web location to change, while still allowing the entity to be found.