how to use sqlhelper dll in visual studio 2008?

This dll is part of the application block for data access.
You can read more about it here -
Microsoft Application Block for Data Access in .NET[^]

Another good link to consider would the Application Block site itself - http://msdn.microsoft.com/en-us/library/aa480458.aspx#entlibjan2006_dataaccessappblock_design[^].

Well I think you must describe your question in more elaborate way.
Anyways what it seems like you are trying to add the reference of a dll in in your vs 2008 project. If so then to add any dll in your project then you can simply add the reference of that dll in your project. In case you don't know the process then you can review the URL.

http://social.msdn.microsoft.com/Forums/en/Vsexpressvc/thread/84deabaa-ae82-47cc-aac0-592f5a8dfa22[^]

Please let me know if anything else you're looking for.

:)