I'm just having the same problem.
I was looking for a linux 64-bits version of bricxcc
I finally found this link :http://www.krizka.net/2009/12/27/starting-mindstorm-nxt-2-0-development-on-linux/
So I wrote a simple hello world programme and compile it with nbc compiler and then dowmload it.
It works correctly. Then I test a program with a cos function (not Cos but cos !) and here i get an error.
It was the same error than when I used the standard firmware on my nxt !But now my nxt have a enhanced firware. The program runs correctly on the nxt if i compile it and download it with my windows computer, but not in my ubuntu computer.
Here is the link of my previous topic with my error (on windows) : viewtopic.php?f=3&t=1795
I'm still looking for a solution for the ubuntu problem.
I foud the nbc 1.2.1r5, but I also have an error, something like : "nbc is not a bynary file"http://bricxcc.sourceforge.net/nbc/release/
So I can't help you for the moment, but I'm also looking for a solution.