I haven't done it so I don't have an examples but you would use OLE automation to "push" data from Access and manipulate the Object model of VISIO. To find help on this topic, you would use help in VISIO and search the MSDN library for articles.
To "pull" data from Access, you should find options from within the VISIO menus.
PS - addressing your questions to me specifically is a bad idea. You lucked out today since I was here when you posted and happened to see the post. Others know more than I do on MANY topics. You don't want them to ignore you do you?