i'm sure you already saw this... but if you boot into your ubuntu system, what does the fstab say about your root partition?
mounting error? [SOLVED]
i'm thinking if you have the issue listed above, try the ext3/ext4 change in /etc/fstab and then try to boot BT again to see what happens?
also, for a second opinion, i came across this:
Hak5 Forums > Backtrack 4 final is giving me some problems that I am unable to solve
good luck with that, be sure to post the solution when you get it figured out, neh?
EDIT: also, could you be a bit clearer on your wi-fi issues? it is entirely possible that you have an unrelated issue there...