Determining whether RHEL4 is registered?

Hi, I have an interesting dilemma regarding registration with up2date in 
RHEL4. I have a yum (yum-arch) repo I want to use under RHEL4 with 
up2date. However, if a system is not registered, I need to comment out the 
following line:

up2date default

in /etc/sysconfig/rhn/sources

I need to do this in an automated way via a rpm I install on the target 
system. Is there some way I can determine the registration state? Perhaps 
there's a utility or tell-tale file I can consult to do this?

The best I could do is run the following command:

up2date --showall

If the system is not registered then a message to that effect is printed 
and the exit code is non-zero. However, I'm not sure what happens with a 
registered system when the network is down.

Maybe I should ask this question on the Red Hat System Administrators' 
list, but I thought I would give this list a try first.

Regards,

Timothy