Actually the Ubuntu 7.10 Alternate install CD has the option to install as RAID. The UI is weird, you have to go in and make a failed attempt to delete a RAID at some point to get it to recognise that there are existing RAID paritions, then you can create a new RAID partition. You can install with RAID from the Ubuntu 7.10 alternate install CD, but in the LMCE install process you will also need the normal Ubuntu Desktop 7.10 install CD as a source to complete the LMCE install. It works OK once you battle the partitioning and RAID UI a bit. It is not nice but not really awful either.
Anyway, having done an install with RAID for my Linux OS partitions, I would advise to not do it. LMCE seems to think that RAID should be reserved for media only, and will treat any RAID devices it finds as a source of new media. Then will create a symbolic link in /home/public/data/other to the top directory of the RAID partition.
So if say your / filesystem is RAID, you get this endless loop as the UpdateMedia service starts at /home/public/data/other where it has put a symbolic link to /, then gets sent up to / where it trundles its way back again to /home/public/data/other/ and finds the pointer to / again "hey a new link to a RAID media storage partition!".... and does this over and over merrily creating lots of symbolic links with very long names on the way (and chewing up IO and CPU resources).
So until I gird my loins and dive into the LMCE shell scripts to fix this bug, don't do RAID for anything but separate filesystems that you will store media on. That's the way LMCE wants it.
(as usual this is from my limited experience and limited amount of hair tearing, happy to be contradicted by people who understand the architecture of LMCE in more detail)