source for building kernel-xen0 ?

Hi,

I am a newbie here, and I have installed fedora core 5, xen, xen0, xenU on 
my thinkpad laptop, follows the quick start guide, I can bring up guest 
xenU, everything works fine, including networking.

now I want to learn more about xen, and want to build everything from 
scartch,
there are some rpm comes with fedora 5, like some kernel-xen-devel package, 
but it only include the headers file, no C codes at all, 

so I googled though every where, but I could ot find the source RPM for that,
the only xen source I can find is xen-3.o.???.src.rpm, which builds kernel
ends with "xen", not "xen0", 

so I am wondering where do I find the source or building xen0 ? or, I should
just use the "xen-3.o.???.src.rpm" ?

thanks,

-- Ping