Uhm, no.
Xen 3.4.x is NOT supported on RHEL5/CentOS5 
!!
RHEL5/CentOS5 includes Xen hypervisor 3.1.2 (+a lot of patches by 
Redhat and from newer Xen versions).
That's the version that is supported by 
Redhat in RHEL5.
I believe xen.org is planning to release at least Xen 
3.4.4 until 3.4 branch is 'forgotten'.
See: 
http://xenbits.xen.org/xen-3.4-testing.hg"6 
weeks ago:   Update Xen version to 
3.4.4-rc1-pre".
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Ah, so at the minute, I'm currently getting my kernel security 
fixes from RedHat, but getting my Xen security fixes from Gitco.
 
This sound ok (Security wise)? The reason why I didn't stick with 
the 3.1.2 version is becuase FreeBSD (My pfsense DomU firewall) won't boot in 
this version.
 
Of course, I'll use Xen 4.x once I get a testbed running nice and 
stable.