Need Current login user Php code for joomla!

[medphoenix]

Hello,
Please If anyone know respond me with the code.
What I want is, I need a PHP code for joomla CMS.
This code should reveal the current login user (session).
I need to put this for greeting the user like as follows:
WELCOME XXXXX!

When the user haven't login yet, It must show "WELCOME guest!"

I especially need JOOMLA 1.5 Code, so I can put this one in index.php of any templates.
Thank you In advance.

<?php echo "Welcome!" ;
		xxxxxxxx;			?>

xxxxxxxx = your code
Edit:
Sorry...no answer on time...I got the answer from another one...So please close this thread