email question

[bike5]

Hi, I have a registration form that sends an e-mail to the person after they submit the form. My problem is the e-mail wont display my strings and html. I have a link sent in the e-mail to activate there account-
In my code it sends the e-mail with

http://www.mysite.com/activate.php?ID=$user_name

The $user_name is taken from the form they used when submitting. Now, in my e-mail, it puts out:

http://www.mysite.com/activate.php?ID=
and thats it. It doesn\'t include the $user_name. How do I get it to include the name? The string $user_name does work in the subject line but not in the body?
And is there a way to get my html to work in the e-mail, becaise it just sends my html as shown html like text.

$mailsubject = "Account Activation for $user_name";//--That works in the subject
$mailbody = "To activate your account, go here: http://www.mysite.com/activate.php?ID=$user_name - - - <a href=\"http://www.mysite.com/activate.php?ID=$user_name\">Activate!</a>";

mail($user_email, $mailsubject, $mailbody, "From:[e-mail]");

Thanks for your help.