Launch Toad and check under Help | Support bundle. The main Toad for DB2 header will note DB2 64 bit client if the install was done for the 64bit client version.
Sample:
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Support Bundle: Toad for DB2 5.3.0.928 Registered Version
IBM DB2 64 bit client
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If it is not noted, then the 32bit client version was installed.
Sample:
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Support Bundle: Toad for DB2 5.3.0.928 Registered Version **********************************************************************
Please note, the initial splash screen for Toad will also note 64bit if it is the version with the 64bit DB2 client.