When booting a DS20 with the kernel image provided on the RH6.0 CD, as well as the alpha RH6.0 boot image, the kernel hangs after initializing the SCSI bus. This can be fixed with a newer version of the kernel, but as of no new alpha boot images none appeared on the updates site. (ftp://updates.redhat.com/6.0/images/alpha)
DS20s do not boot uniprocessor kernels, currently. We're working on getting boot images for them.
We have posted the new SMP boot kernel which should solve this problems for you. ftp://updates.redhat.com/6.0/images/alpha/kernel-smp.img