If its word processor documents you care about, you'll be able to do this with docx4all, but right now that will take a bit of effort on your part.
By the sounds of it, you might want to run docx4all as an applet, rather than an application. And you'd need to pass it the URL of the document.
Also, to edit a .doc (as opposed to a .docx) it first needs to be transformed to a docx. Alfresco could be made to do this, perhaps if this version of OpenOffice was available to it.
