New Xen VPS Lacks Modules

CentOS 5. I can't run iptables.

/lib/modules is empty.

In /var/log/messages, this line is repeated many times:
modprobe: FATAL: Could not load /lib/modules/2.6.18-5-xen-686/modules.dep: No such file or directory

iptables -L gives this:
iptables v1.3.5: can't initialize iptables table `filter': iptables who? (do you need to insmod?)

Perhaps iptables or your kernel needs to be upgraded.

Is this something I can fix via yum install xxx or some other way, or is it something my provider has to do?

I tried yum install kernel-xen, but that installed 2.6.18-53 and modprobe is looking for 2.6.18-5