how to recompile already installed gentoo to run on different machine?

Hi!
Anybody tell me how can I solve that problem? For example migrate from 
x86 to AMD64.
I guess, it requires cross-compiling for both new kernel and all 
applications, but some how-to link or quick summary of this task would 
be greatly appreciated! (I was hoping, that this is good place for such 
technical question, even if not most appropriate one)

-- 
Jan


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Linux-crypto:  cryptography in and on the Linux system
Archive:       http://mail.nl.linux.org/linux-crypto/