I re-introducted this snippet on my forum. I went to Hotscripts - http://www.hotscripts.com/Detailed/61284.html
then did a search on 'Recommend' then clicked the first Tell a Friend PHP Script block and just followed it to the zip file, which contains all the files you need.
Once you extract the files you should edit the 'header.php' file with details of your site. You'll probably want to change to the logo.gif and admin gif to your own as well.
Then upload all the files to a directory like 'tell'
Also per the included instructions you'll have to chmod the conf.php to 777.
Once you get into the admin section, then you configure the settings, verbiage you want to go out to the friends of your members, the URL of your site and return URL after they submit their friend's email list.
Here's what it looks like - http://www.avalanchestyle.net/tell/tell.php