I just got my hands on a Toshiba satellite p855-33C and had a similar problem. After entering the BIOS to disable "secure" boot and switching to CSM mode from "advanced" tab, I was able to boot Ubuntu 12.04 64bit from a bootable usb stick created as per ubuntu instructions. I then inserted the stick on a usb 3.0 slot and powered-up.
I chose "Try without install" and the system came-up in 73 sec. Pretty decent for a live usb system. The start-up script even detected that I was using a Greek keyboard added the Greek layout to the list of available layouts and offered to change the default folder names (even though I selected English at start-up for system language - is this cool or what?).
On your dual-boot question I suppose that the only way is to manually switch the BIOS settings each time you want to switch OS, as this is actually a design issue (win8 will not boot otherwise - congrats to micro$oft for "improving" the desktop experience once again). Now as far as the win8 partitions are concerned, I am pleased to report that they are visible through Nautilus like any other normal partition. Just mount and explore/explode.
On a broader note, most of the hardware seems to be working properly. Bluetooth works fine, LAN is functioning properly, Function keys to increase - decrease volume and play/pause prev/next song work fine, wifi on/off doesn't work, brightness control not working. Also I'm having some trouble with the sound. Webcam works fine.
Having said that, most of these issues should be resolved with a full install and update of h/w drivers. I just ordered a Kingston SSD to replace the internal hdd and I'm itching to do the complete install :-)
Hope this was helpful. My apologies for the lengthy post.
Note: In order to run the BIOS setup you need to boot to win8, then hold "shift" key while selecting "Shutdown" to force a complete shutdown. Then switch on the computer and press "F2" to enter BIOS setup utility.