This is a lame workaround to get excel plots as vector images.
Select your Micro$oft Excel plots. Copy. Open Micro$oft PowerPoint. Paste-special as enhanced metafile (emf) into an otherwise empty slide. Save your PowerPoint slide as an "other format" file (on the 2007 menu), and choose "emf" (an enhanced windows metafile! wow!). Import your emf file into inkscape and ungroup the object. Delect all the a4-sized crappy blank space from the image and enjoy.