WinXP X64 License

Hello,

I own a copy of WinXP Pro Retail, and I am not using it. A friend just
acquired an Athlon 64 System with out an OS. I was going to give it to
him, but I want him to use the full 64 bit functionality. I am curios;
can the key I have for the 32bit version of winxp work on the x64 copy,
and will it work on the trial download?

Thanks,
Phant