There is not really a certification path for the MOSS 2007 certifications. There are 4 related exams MOSS Configuration (70-630); MOSS Development (70-542); WSS Configuration (70-631); WSS Development (70-541);
Each of these exams stands on their own and passing any of them will earn you the related MCTS certification.
If you are ready to move on to the SharePoint 2010 exams then there is a progression of exams/certifications that you can work through. For instance, if you choose to work through the SharePoint 2010 Configuration/Adminstration track (rather than the
Development track) then you could work through the following certification tests:
70-667: TS Microsoft SharePoint 2010, Configuration
70-668: Pro: SharePoint 2010, Administration
Then you could even work towards the Microsoft Certified Architect for SharePoint (this is currently in development)
For all of the information on the SharePoint certifications see the following:
http://www.microsoft.com/learning/en/us/certification/cert-sharepoint-server.aspx
