It always bugged me that Katanas were used in one hand, as they are more often than not used as two handed weapons. (They were/are used on-handed occasionally, but rarely, and never by themselves.) So I tried making a two handed Katana, except it equipped at the hip and I drew an invisible sword off my back. It took me a while to figure out how to get the katana to equip on the back, but it turned out to be very easy.
First, you will need NIFSkope, which you can get from here:
http://sourceforge.net/project/showfiles.p...ckage_id=170735
Open up NFSkope, load a weapon mesh of your choice, and hit F2. Click on the plus sign next to '0 NiNode' in the BLock List menu, which should open up some more options.
Then, click once on 'NiStringExtraData' in the Block List menu, which should bring up a few options under the Block Details menu. There should be one called 'String Data'. This will have a value of either 'SideWeapon' or 'BackWeapon'. Change it to wherever you want it to equip, and make sure that you use the appropriate weapon type for the equip slot. (Two-Handed for Back and One-Handed for side.) Then, just make sure to save the .nif file. That should be it. Feel free to PM me if you have any questions, and if this was already posted, sorry.