When you create a live-usb backtrack with unetbootin, it is not running on a dell mini9.
The operating system will is not start. The problem was already present in the beta.
Nvidia GeForce GT 320M
BT5-64bit x WIN7-64bit DualBoot
Problem solved. The error came from a problem between unetbootin and ubuntu 9.10 alpha 2.
Sorry for the misunderstanding.