It’s actually very easy to boot from USB on the Asus EEE box B202 when you know how it’s done. When your trying to figure out though you would probably be forgiven for throwing the PC out a window in a very very tall building.
Firstly. Boot into the BIOS of your PC. Disable all boot devices excluding the hard drive.
Now reboot the PC with the USB drive attached. As the PC starts continually press the F8 key to start the boot menu.
Select your prefered USB device.
Note this shouldn’t need to be done. Under the boot tab there is a menu labeled mass storage devices. In here it shows the card reader as well as your USB key. You can then select the primary USB device for selection in the boot order screen. The problem is that in my experience when you selected the primary USB device to be anything other than the card reader the hard disk would intermittently become unavailable in the boot preferences screen. I can only deduct that this is a bug somewhere in the BIOS but either way it’s very frustrating.
I hope this helps.