Use SPD 2007 to open 32 bit site like wss or SP 2007. If can not open WSS 3.0 in SPD 2010 or SPD 2013.
See this similar thread for you ref here:
http://social.technet.microsoft.com/forums/en-US/sharepointcustomizationprevious/thread/fea6b329-2e57-442e-ad8a-25fcfcfa06b1
Hemendra: "Yesterday is just a memory,Tomorrow we may never see"
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