Thanks for the advice on instaling on 64 bit.
The killer feature for me on WHS over all other server products is the storage pooling, called drive extender I think. It basically allows you to add hard drives to the storage pool to create more room, and, where it scores over RAID for me is that the files are stored on standard NTFS partitions, that can be accessed directly should the need arise. For example, my main server has 12 500GB harddrives in RAID5, giving me 5TB of storage space, it is fault tolerant to the extent that I can lose one drive, and still retain my data, lose two drives and it is all gone. With WHS I would have slightly more storage space, lose one drive and I would lose 1/12 of my data (if mirroring was disabled), lose two drives and 2/12 gone, but not all. For my needs this is far better as my data is mostly ripped DVDs that I can rerip, however I do not want to have to do a full 5TB of them again!
So really, this is the main feature for me of WHS, and none of the other server editions, including 2008 have it. Also no need for costly hardware raid cards!