After extracting sqldeveloper-2.1.0.63.73.zip and executing sqldeveloper.exe, I received following error
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Oracle SQL Developer
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Unable to create an instance of the Java Virtual Machine
Located at path:
<SQLDEVELOPER>\jdk\jre\bin\client\jvm.dll
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OK  
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Follow this workaround to fix this issue…
Open ide.conf file from

<SQLDEVELOPER>/jdev/bin/ide.conf
or
<SQLDEVELOPER>\ide\bin\ide.conf

In this file, change this line :
AddVMOption –Xmx512M to AddVMOption -Xmx256M
Now, you can launch sqldeveloper.exe without error.