An important warning about Tell a Friend scripts:
Unless they are part of a larger script package that is REGULARLY KEPT UP TO DATE don't use them -- even if they have a captcha feature. Hackers can use code injection to circumvent captchas. Then they run the tell-a-friend script to relay/broadcast spam.
Most stand-alone "tell-a-friend" scripts are security vulnerable in this manner and should not be installed in any web hosting account. You could have thousands of messages sending from your account and never know it. Soon the your account and domain is blacklisted (and possibly the entire LinkSky server) world wide and your service could be impeded for an extended period of time.
Also -- It is very important to check weekly for updates from your script package publisher. Many developers have a forum of some other kind of service that you can subscribe so that you will receive notices of updates, but don't rely on that completely. Improved security is almost always part of every update.