I have a Tell-A-Friend form set up on my site. I found that if I type the URL in with "?www.someothersite.com" at the end, it can also reccommend that other site [in case you're wondering, the extension before the question mark is .php] Spammers can access it & use the form to spam god knows how many other sites.

Is there a good way to prevent that from happening?

like this?
http://www.anders.com/cms/75

I'm not sure that I understand that site.

Did you read this link from that first url - http://www.anders.com/projects/sysadmin/formPostHijacking/ That tells you what you can do about it.

I see it now. I'll have to really read it, because I'm a little confused.