Hi,
According to Microsoft,
MCAD - Microsoft Certified Application Developers (MCADs) use Microsoft technologies to develop and maintain department-level applications, components, Web or desktop clients, or back-end data services.
MCPD - The Microsoft Certified Professional Developer (MCPD) credentials distinguish you as an expert Windows Application Developer, Web Application Developer, or Enterprise Applications Developer. These credentials demonstrate that you can build rich applications that target a variety of platforms using .NET Framework 2.0.
so bascially, if you go for a MCAD you are an application developer(develop) using microsoft technologies, and if you go for a MCPD you are a professional developer(design and develop).
Both are important depending on what you want to do, i preferred MCPD as that certifies my as a design and development guy.
These are Microsoft certified exams, i,e you get these designations after you pass the microsoft exams.
use this link h**p://www.microsoft.com/learning/mcp/certifications.asp
All the best.