Last week I upgraded a Virtual Center server from Win2003 & MSSQL 2000 (32-bit) to Win2008 & MSSQL 2005 (64-bit).

During the installation of vCenter it asked for a 32-bit ODBC even though all the new systems was running 64-bit.
After a some time on Google i found that Windows 64-bit also includes a 32-bit version of the ODBC.

To set up a 32-bit DSN launch the 32-bit version of the Data Source Administrator. It is located at:
%systemdrive%\Windows\SysWoW64\Odbcad32.exe

Also se
http://www.vmwarewolf.com/32-bit-odbc-dsn-for-vsphere/