Persistance in flash drive install.

Im trying to install BT to a 2g flash drive… I boot it from disk install it like you would if the flash drive was a HD, install the bootloader and from there… nothing. It wont boot on any computer i've tried three and each one i've tried has a separate BIOS version. I have it set to boot from USB, and the one i expected to work says its invalid. I found a tut, but it says persistence is outside the scope of it. I want the OS to boot from flashdrive and then be able to save documents to it and have it load the same on other computers.

i usually just use isotostick.sh to convert a linux cd to a usb cd, i've only created customised versions of ubuntu and put them on a flash drive but it works for me. https://help.ubuntu.com/community/Installation/FromUSBStick

also this seems to be discussed in more detail here: http://forums.remote-exploit.org/showthread.php?t=10172