Try this
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To uncompress a bzip2 file, execute the following command:
bunzip2 filename.txt.bz2 (where filename.txt.bz2 is the name of the file you wish to uncompress)
The result of this operation is a file called filename.txt. By default, bunzip2 will delete the filename.txt.bz2 file.
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from
http://www.linuxheadquarters.com/howto/basic/bz2.shtml
oftentimes, it is .tar.bz2 and the following command will leave you with a whatever.tar file. If this is the case try tar -xvf whatever.tar
/me shudders @ the thought of Roothat, but thats just my 3 cents