Create your graph/chart using Microsoft Excel:

Upload your Microsoft Excel document into a sharepoint document list:

Select your graph/chart by clicking on it, and press the save as web page menu item:

Before saving, select the "publish/Republish" radio button, set your title and file name:

Configure your publishing settings, by pressing the tools menu item in the upper right hand corner of the dialog:

I've found that selecting "Allow PNG as a graphics format" will improve image quality, but you should configure your settings based upon your needs:

Press the publish button.  Make sure you have the "AutoRepublish..." checkbox selected if you want your chart to be updated everytime the Microsoft Excel document is updated.

Once published, you will see your chart saved off as a web page in your document list:

 Go to the location on your sharepoint site where you want the graph to appear and modify the site content... then and add a "Page Viewer Web Part" to your site:

Drag this onto the desired location on your site:

Open the tool pane for this web part and setup the web page reference (take the url of you publish graph/chart webpage):

Your graph/chart should be visible on your site... and will resynchronize itself every time the document is updated!

Team VivaBig (Inetium's SMS&P, Application Development Team)