It is not Vista to allow to boot from external, it is system if it does not have that option in bios. Check in bios page, boot section, see if you can set system to boot from external?
Also, when you created image using True Image Home, did you also create boot disc? which later you can start up system with it and map the image and then restore to? Below is procedure:
http://us1.download.acronis.com/pdf/TrueImage11_ug.en.pdf