Go with a blank dvd to burn the iso as CD i think don't have enough space for BT4.
then just use the boot with CD at BIOS and boot your backtrack.

hope it helps

A clean install will go smothly. if you try to upgrade and don't know what you are doing something will go a miss and won't work.

Ok if thats not working then try this.
Get the latest ver of backtrack iso and then use unetbootin application from sourceforge.net and use it to mount the image to the USB. then go to the Bios and...