You need the 32-bit driver installed when:

- you use BIDS for development and debugging

- you want to run a package by calling the 32-bit version of dtexec.exe directly

You need the 64-bit driver installed when:

- you need to create a Linked Server in a 64-bit version of SQL Server

- you want to run a package using the 64-bit version of dtexec.exe (the default for SQL Agent job steps using the SSIS step type)

The different ODBC managers can be found here on your 64-bit server:

- The 32-bit version of the Odbcad32.exe file is located in the %systemdrive%\Windows\SysWoW64 folder.

- The 64-bit version of the Odbcad32.exe file is located in the %systemdrive%\Windows\System32 folder.

There may be some crossover when viewing User DSNs: http://support.microsoft.com/kb/942976