This is my way to install bt3 into Usb.

What do you need?

Usb Stick 1 or 2 gb ( I have verbatim)
Download (i am not allowed to post url)
Bt3 cd image bt3-final.iso
Fixkp2 (go to the website pendrivelinux and search for usb-knoppix)
Ultra iso or daemon tools (or any other to open or extract iso)

After you download Bt3 cd image extract (or burn) the iso to your computer.
After you download Fixkp2 install it (a usb-knoppix folder is created).
Now insert the usb stick. Right click - Format. For File system select Fat32 and for Volume Label BT3. Click start and the format is done.
Ok now we are ready.

Open your bt3 cd image (that you have extracted) and copy the folders Boot and BT3 that are inside. Move this two folders to your usb drive. Now go to the folder USB-Knoppix (that is created from installing the Fixkp2) and copy only syslinux and makeboot to your Usb Stick. Now go inside your Usb Stick drive and click makeboot (FOR VISTA USERS RIGHT CLICK AND SELECT RUN AS ADMINISTRATOR). A command prompt is opened and you just press enter. Thats all. Now reboot your computer and select boot from usb (to bios) and enjoy your BT3 Usb.

Thank You