(1) Amending the Ubuntu GRUB configuration to contain a stanza for TC should work just fine (assuming it contains the correct references to the TC kernel and initrd).
(2) What Curaga meant with reply #2: To support ReiserFS a kernel module (i.e. 'reiserfs.ko.gz') is required that is not included in the "official" initrd (but could be installed via tce-load -wi filesystems-KERNEL into a running TC system). You'll probably wish to have said module available early in the boot process to be able to mount the ReiserFS file system. Therefore you'll have to create your own initrd into which you've copied that module. This process is known as remastering and several explanations are to be found in the Wiki (as well as in many forum threads).