To vladlp:
If you want to compile for 64-bit windows xp. The best compiler is VS2005 which support compile 64-bit project directly.
VS6 and VS.net can be used also. But you should install 64-bit platform sdk and modify the project setting manual.

I faced this problem 1 month ago
The big problem is not the compiler itself but the libraries.
The first try was to use DDK (which is the only non beta stuff that containd AMD 64 bit compiler)
Since DDK focuses on drivers I got easily libraries problems and problems related of adapting projects to DDK building env.
Normally the AMD64 support should be delivered with Platform SDK
It seems there is a platform SDK (non public) beta that has AMD 64 support. Unfortunately I couldnt get it. Im still wondering why they dont realease a SDK that includes AMD64.
The latest VSNET 2005 has the compiler and the libraries for a lot of targets including AMD64. So I had to install a lot og Gigs only fot this AMD64.
It sucks but its the only way
But remember the best way is to get that platform SDK( I post the number later cuz I dont have it here) that has AMD64