Loading content into html/css page

what would be the best way to have an external file contain the content and have it load into an html page? like a text file or something so that a site owner could make small changes to the text file and it would be brought into the html page? also, maybe if this is done, the same info could be loaded into flash as well, like an html and flash version of a website could share the same content (though the flash part is optional). this seems like it should be possible, but i just don’t know how to go about doing it. a free solution is definitely preferred.