There is a way to access BIOS (UEFI actually) and to boot from USB drive.
SP3 is a normal x86 based PC, just in a different form (with no keyboard and touchscreen), I see no reason why they'd lock the bios or boot loader on such an expensive device meant for IT professionals (among others). And if you can boot from USB, you can most probably install any OS you want (
Ubuntu for example).
However, I'd suggest to install the TH into a virtual machine, because it's a preview, not eve beta, which means it WILL BE full of bugs and not stable for day to day use.
edit: x64 is an extension of x86. x64 based PC is still a x86 based PC.