just use lilo it is included in bactrack
it might be a good idea to have a look at the wiki there is an install video on how to install bt2 it will also work for bt3 beta, done by muts
http://backtrack.offensive-security....on_.28movie.29
transcript of movie is here:
http://backtrack.offensive-security....cript_of_movie
If you just have to use grub then have a look at the wiki here:
http://backtrack.offensive-security....boot_from_grub
Next time please try and use the search function of here and or google



