you are using red hat
So you did buy a license ??? RIGHT !!
rhel is not free
a license IS REQUIRED to install software updates and SECURITY FIXES !!!
so use your paid for tech support
FOR THE paid for RHEL 5
yum search qemu
-- if it is there ( should be)--
yum install qemu-kvm
you DO KNOW that the very very new 13 ( released yesterday)
will most likely not install on the much older rhel 5.3 ?
is your 5.3 install fully up to date ????