Suggest any good site/resources for design of client/server,n-tier architectures??

Hi, Most of them comes with experiences. That is why a company will hire someone who have 5 - 7 years of experieces to become a software architect instead of 1 or 2 :p There are a number of pattern and practices by Microsoft - you can take a look... that is all i can recommend... except you hire some consultant for help :) http://www.microsoft.com/resources/practices/default.mspx Cheers.

Is there any tools/process to validate my design.How can discreminate whether a design is bad or good,is it comes from experiance????

MSDN is the best to start with!! There are other plenty of them, like CodeProject.com, etc