phpBB Migrate Failed

i tried to migrate phpBB from my freebsd machine to byethost.
the procedure should be:

*backup phpbb files from my machine
tar czvf phpbb.tgz /phpbb
*backup phpbb database from may machine
mysqldump -u root phpbb>somefolder/phpbb.sql
*ftp upload phpbb files
*restore phpbb database by phpmysqladmin or phpbb function
**phpbb function -> failed
**phpmysqladmin -> OK!

but my forum is full with unknown codes like [????]
there is a language format proplem in my phpbb forum.

my original phpbb forum data saved by mysql is coded by BIG5 ( in mysql is LATIN?)
when i restore the database i should choose the right coding method, so i tried.
by selecting big5 but still failed.

when i looking for some clues on google,
find out this proplem is a pain in the ass for a lot of chinese phpbb users.
the proplem is trasfer BIG5 into UTF8.

still looking for best way to convert the database…