A few things:
1.) N810 is ARM arch, that Xubuntu ISO is compiled for x86.
thus not gonna work, period.

2.) Simply dragging a linux ISO onto a thumbdrive isn't sufficient to make it bootable. A few "hacks" need to be applied depending on the distro.

3.) As far as I am aware the N8X0 can't boot from USB.
I once uncommented the line in the bootmenu script about usb booting, flashed it to device and bricked my install. In order for this to work the USB OTG port (w/ proper cable) would have to be switched to host on boot and this is (not currently) possible due to host mode being triggered in software.

Things you should look into:
a.) USB OTG cable if you haven't done so already
b.) connecting a usb hdd (with a y-cable or similar)
c.) usb wifi injection
d.) usb camera; usb rf scanner
e.) using the n810 as a thumbdrive
f.) Mer (dead), Meego (unreleased), and
the most helpful suggestion of all

* Qole's EasyDebian chroot * or * Penguinbait's KDE chroot *