[CentOS] RPM rebuild, cross compiling from x86 to x86_64

Hi

I want to recompile some RPMs (my own) for x86_64 arch from my i386
compatible build host (because of hardware restriction/funds).Is anyone
ever done this ? After a google search, it seems not so easy... i just
found this: http://www.speedblue.org/cross_compilation/ but haven't
tried it yet (i would have to convert these to RPM first).

How is it done for Centos SRPMS rebuilds ? is it a different
hardware for each target arch ?


Thanks !

-- 
Martin