The release V4.0 of sql developer is available for download : oracle.com/technetwork/developer-tools/sql-developer/downloads
The doc is there : docs.oracle.com/cd/E39885_01/index.htm
I requested some time ago a 64bit Windows version with JDK on Oracle SQL Developer Exchange and once again it got accepted.
Okay, I have on my PC two Oracle homes : one for 32 bits and one for 64 bits. The 32 bits is first in PATH.
When I start SQL Developer, I could not use the OCI thick driver which is required when connecting via LDAP or TNSNAMES. SQL Developer was failing with error :
ocijdbc11.dll: Can't load IA 32-bit .dll on a AMD 64-bit platform
Apart from changing the path in the Environment variables or in .bat file, it is possible to add the following line in sqldeveloper/bin/sqldeveloper.conf (where dbhome_2 is a 64bits home):
If you need to connect to Sybase ASE (or MSSQL), download the driver here : http://sourceforge.net/projects/jtds and add it as Datasbase/Third-Party Driver
For MySQL go there : http://dev.mysql.com/downloads/connector/j/ and download the Platfrom Independant ZIP file.