Xen Virtualization in redhat kernel

Hi

Can some one please tell me what is the significance of below kernel version

title Red Hat Enterprise Linux Server (2.6.18-308.el5xen)
root (hd0,1)
kernel /xen.gz-2.6.18-308.el5

what I have downloaded RHEL 5.8 version and installed on physical servers and now its showing an extension of Xen . and due to this some of the rpm installation fails