Which error are you getting?  Please post the output from these two commands:

echo $PATH       # Remember you need a $ to access shell variables

which g++

Your path should be separated by : (colons), not new lines.  If you get a valid answer to "which g++" add that to your path by appending a colon and then that directory to the path.  For example, my path (in TM) is 

/Users/bmf/.rvm/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin

When I enter "which g++" into terminal I might get (for example) 

/opt/extra/stuff/bin/g++

So my I would change my path in TM to 

/Users/bmf/.rvm/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/opt/extra/stuff/bin

Note: my g++ is in /usr/bin.  That is by default in the path.  Rather than muck with your PATH, I would go with Allan's advice and make sure you have it installed correctly.  If 'which' doesn't find it and you didn't purposely install it into some weird place, it probably isn't installed.

Brandon