how to make user logged in automatically

[spatel]

thanks for the website compliments,

it works for posting username, password and three other feilds on login.php?do=login

but the problem is i have to store the password in plain text format somewhere to post it on the login.php page as hidden variable or session variable, and I dont want to do that for security matter.
I am looking for something same as calling datamanager object to insert into database, same kind of mechanism or idea to check the username and password and make user logged in.

<form action="login.php?do=login" method="post" >
<input type="text" name="vb_login_username" id="navbar_username" accesskey="u" tabindex="101" value="User Name" onfocus="if (this.value == 'User Name') this.value = '';" />

<input type="password" name="vb_login_password" id="navbar_password" tabindex="102" />

<input type="hidden" name="securitytoken" value="57c07616d871c2c5012061b399dedc6fe3767bf7" />
<input type="hidden" name="s" value="" />
<input type="hidden" name="do" value="login" />

<input type="submit" class="button" value="Log in" accesskey="s" />
</form>

I want automatic login so need to use hidden variable here instead of textbox, and it works but storing password in plain text kills me, and also it transfer to the page I go to the forum(history page), I need to have forum index page always when user is transfered to forums from normal website,

Thanks