Where can I get Perl 64 bit, other than Active State?

I don't think you can on Windows.
If you install the 64-bit build of ActiveState and also install the freely available "Microsoft Platform SDK for Windows Server 2003 R2", you might be able to build DBD::Oracle for that build of perl.

Once you've installed that SDK, you need to run C:\Platform_SDK\SetEnv.cmd /XP64 /RETAIL (the exact command depends upon where you've placed the SDK) in order to set up the environment variables so that the compiler, etc are found automatically.

I have no idea whether that approach will be successful :-)

Can you use a 32-bit build of perl and DBD::Oracle on your machine ? If so, that would probably be the simplest way to go.

Cheers,
Rob