You should only see the option of these two kernel types if you're running on a multiprocessor system. esmith is the default, SMP enabled, kernel for these systems and esmith-up is a fall-back, Uni-Processor, kernel for if you have trouble running the SMP kernel.
Having said that, some people have noted that some recent P4 motherboards have been incorrectly identified as being SMP capable by the installer and get the SMP install. It's a simple matter of editing /etc/lilo.conf and re-running lilo with the uni-processor kernel as the default. You may also see this situation if you have an SMP capable system that only has one CPU installed.
Gary