If you are talking about
chipv's Map XML Wizard, which lets you create or edit XML by pointing, clicking and typing, keep in mind that you can use a file on your machine by using the Browse button on the second line of the toolbox (or simply typing in the name of the file in the box next to the Browse button) and then pressing Load File.
The
XML Tool, however, can only access files from an HTTP file sharing site. (The Wizard can do this as well, via the box next to the Load XML button.)
I use fileden.com. There is a no-cost account deal (popups, of course), and it is quite easy to use. Plus, I
think it is a little better at coping with moving files around on the site while not breaking the links that you post.
Once you have an account, use the Upload function to transfer files from your computer to fileden.com, then use the Files function to get to your uploaded files via the Fileden file manager. RIght-click a file to see possible actions. Click Properties... to get a dialog box with details, then click URL to get another dialog box with the URL in a text field, already selected and ready to be copied and pasted where needed. Clicking BB Code works similarly, but provides just the right codes to put into a post (in the Foundry, say).