I'll start with an out of the box team site at the top level site of a new site collection. Out of the box other than the change I made to the Title, Description and some text on the front page.

I almost always use Site Actions> Edit in SharePoint Designer so I'm in the right site.

You can put the file in the site pages library if you like but I'll put mine here.

Choose File>XML

I named mime Books.xml since the XML file I'm using is a list of books. After I name it I click the name to open the file for editing.

Microsoft offers a great sample XML file called books at this URL: http://msdn.microsoft.com/en-us/library/ms762271(VS.85).aspx but I could have used any well formed XML document. I just went to Microsoft.com and searched for books.xml

I click the edit tab in the ribbon and then click verify well formed XML which is a very handy tool to be included.

As long as the file is all right as indicated by the message I'll click OK otherwise i would have had to work with the file a bit first.

Save often in SharePoint Designer 2010.

I just right click the tab, Books.xml and choose close.

Now that I have my file I'll configure it as a data source. It might actually show up in the data sources list since it's an XML file but i want to configure security and give it a name.

I'll be using Windows authentication so i choose the radio button as shown.

I'll name mine BooksXMLFile and be sure to choose that vs. the raw XML file when adding a Data View. When I'm done i click OK.

I choose File>ASPX page.

I name the file Books.aspx and then right click on it and choose Edit File in Advanced Mode.

A Short cut is to hit escape and then delete when your mouse is in a white area on the page, but delete the form tag for sure.

I select the Style Tab in the ribbon, and then click Attach and Choose the Default Master Page.

Once again i go back to the PlaceHolderMain and grab the glyph and choose Create Custom Content.

I be sure to place my cursor within the now editable PlaceHolderMain and click the Insert Tab on the Ribbon.

I choose DataView> BooksXMLFile (you might have to scroll down) , If it just goes in, it's cool, it does happen sometimes, but more often than not….nothing happens.

By the way if your data went in you can stop here because the rest is only for if nothing happened. But if nothing happens after completing the steps above, in other words your XML data isn't showing, then click View in the ribbon and then click Data Source Details.

Every once in a while that does the trick, but if it doesn't you can make sure your cursor is in the PlaceHolderMain and then choose the Insert Tab and click the Web Part Zone Icon in the Ribbon, this inserts a traditional web part zone into the PlaceHolderMain.

Once the Web Part Zone is inserted you can click the Data Source Icon in the ribbon and choose BooksXMLFile, you might have to scroll down.

Always remember to Save often when using SharePoint Designer.

At this point even if something happens I default to Masters Content using the glyph for PlaceHolderMain I choose Default to Masters Content.

Then I try again. Using the glyph for PlaceHolderMain, select Create Custom Content.

Place the cursor inside of the PlaceHolderMain, Click the Insert Tab in the ribbon and click save.

Just like before.

Not sure why this works but it seems to work every time i try it. I'm not even sure how i figured out to try these steps. Sometimes it's just best to know it works.