64-bit on A64 running 32-bit

[David Rasmussen]

If I am running Windows XP or some regular 32-bit Linux distribution, 
can I still use gcc 3.4.x to compile a 64-bit A64 version of my code?

I have a program that uses 64-bit integers heavily, and I would like it 
to utilize 64-bit mode in A64, even if this A64 is running a 32-bit OS.

Is this possible? Or is 32-bit and 64-bit entirely different "modes" on A64?

/David