The directory is /usr/bin. It is not visible through cPanel > File Manager or any FTP client. It is a public directory containing many executable programs which you can run, but you can't write any files into it.

How have you determined that you are still at PHP 4.4.8 rather than PHP 5? IIRC, if you can switch between the two, it will still say "4.4.8" even though you're on 5. Try some PHP 5-only code and see if it works or fails.

You can run the following to see if you're on PHP 5. Put this code in a file named public_html/test5.php and run it http://www.yoursite.com/test5.php:

<?php
if (stripos("Am I on 5?", "i")) {
  echo "Yes it works.";
} else {
  echo "No, it doesn't work.";
}
?>

If you get an error that the function stripos isn't found, then you're still on PHP 4. Otherwise it should say "Yes it works.".

/ is the Unix/Linux "root" of the file system on your server
/home/ACCOUNTNAME/ is the top of your site's files -- this is where cPanel > File Manager or an FTP client dumps you
/home/ACCOUNTNAME/public_html/ is the top of your Web site (where index.html or whatever is found)
/usr is a publicly readable, but not writable directory with various things customers need
/usr/bin/ is a directory below /usr, holding something like the php executable

There is no "URL" for /usr/bin. You can't get to it from the Web. It's on your server.

Edit: forgot closing ?>

It sounds like you're still running on PHP 4. How did you enable PHP 5 -- did you click on "Enable PHP 5" on cPanel? That may wipe out your existing .htaccess file, so be sure to save a copy of it. Were you missing ".php" at the end of the AddHandler line?

If you have SSH access (command line access), just do ls -la /usr/bin to get a listing of that directory. If you don't have SSH (you'll know you don't if you didn't pay extra for it), make a one-off cron job. cPanel > Cron Jobs, Advanced method, enter your email and M * * * * in the boxes (M is the current minutes past the hour plus 2 or 3). For the command to enter, again ls -la /usr/bin. Save. The command will be run in a couple of minutes and the listing will be emailed to you. Delete the cron job you just created, so it won't be run every hour.

Sounds good!