To have a link switch tabs, you must call the showPanel() function of the Spry Tab Widget. The syntax goes tabPanelName.showPanel(index); The index of your tabs starts at 0 and moves up 1 for the next tab. In this case Tab 2 would have an index of 1.
The code for the link below looks like this: <a href="javascript:TabbedPanels1.showPanel(1);">Click Here to Switch to Tab 2</a>
To download the source in a ZIP file follow this link.