How to customize message after login

hi,

i have created a login box at header file, wgich code is as follow:

<form name=”loginform” id=”loginform” action=”<?php echo get_option(‘siteurl’); ?>/wp-login.php” method=”post”>
Username
<input type=”text” size=”20″ tabindex=”10″ name=”log” id=”user_login” />
Password <input type=”password” size=”20″ tabindex=”20″ name=”pwd” id=”user_pass” />
<input name=”wp-submit” id=”wp-submit” value=”Login” tabindex=”100″ type=”submit”>
<input name=”redirect_to” value=”<?php echo get_option(‘siteurl’); ?>” type=”hidden”>
<input name=”testcookie” value=”1″ type=”hidden”>
</form>

which works fine and show a message after login is “Welcome, admin. [Log Out]”

but i want to change the message as my own. like(Hi, admin. You are welcome to our website..)

anyone can help please?