SQL Server offers RLS/CLS - short for Row Level Security / Cell Level Security. As I understand it RLS/CLS offers similar funtionality of what is called Virtual Private Database in other technologies.
Check it here... http://technet.microsoft.com/en-us/library/cc966395.aspx
Hope this helps.
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Pablo (Paul) Berzukov
Author of Understanding Database Administration available at Amazon and other bookstores.
Disclaimer: Advice is provided to the best of my knowledge but no implicit or explicit warranties are provided. Since the advisor explicitly encourages testing any and all suggestions on a test non-production environment advisor should not held liable or responsible for any actions taken based on the given advice.