do i need to rewrite a 32bit software to work at 64bit OS
do i need to rewrite a 32bit software to work at 64bit OS?
and which vista edition can use to write .net software?
The rewriting part depends on your programming language. For .NET, you will have to inspect issues such as pointers, as they work differently on 64-bit from 32-bit. For writing .NET software, you need any version or edition of Windows since Windows 2000, so any edition of Vista should work fine.
Kea at 2007-9-6 >

Check the MSDN .NET documentation, it's all in there. Here are som URLs:
http://msdn2.microsoft.com/en-us/netframework/aa569597.aspx
http://msdn2.microsoft.com/en-us/library/ms241064.aspx
As .NET programs actually execute natively (though JITted), they don't scale automatically between the modes, so you will have to recompile.
Kea at 2007-9-6 >

Yes yo can, but you cannot run it or debug it in the 32bit OS. You just have to create an x64 configuration in your configuration manager to specify the platform (You have also the chance to create an Itanium configuration also).