First, make sure that you really want to get the MCAD certification. The MCAD and MCSD certifications are for older .NET v1.x technology (Visual Studio 2002 and 2003). The MCTS and MCPD certifications are for newer .NET v2.x technology (Visual Studio 2005). The MCTS and MCPD exams will be updated for .NET 3.0 when it is released. Unless you are only working on older .NET code, consider getting the MCTS/MCPD instead of the MCAD/MCSD.
As for the specifics of each exam, the best source of information is Microsoft's Web site.http://www.microsoft.com/learning/mcp/mcts/http://www.microsoft.com/learning/mcp/mcpd/
If you plan to upgrade from an MCAD or MCSD on .NET certification to a Microsoft Certified Professional Developer certification, you do not need to first obtain an MCTS certification. You will earn the applicable MCTS certifications when you pass the upgrade exam(s) for MCPD: Windows Applications Developer, MCPD: Web Applications Developer, or MCPD: Enterprise Applications Developer.