You may have to use the
http:// rather than just a straight www. Depending upon the email program. If you are using Windows Live mail, Outlook Express or Outlook you can type something like: Sally's Website then highlight it and click the little 'world' on the taskbar (usually the second last icon). That will open up a box for you to input the actual url of the website.
Some web based email programs don't allow linking due to the dangers of phishing and viruses. In that case, the person on the receiving end can just cut or copy it and paste it into the address bar.
Hope this helps...
Hugs, Didi