how to hidden and replace html block with session?

[krht]

If user press (sign in) to my site. (login block) will be hidden and replace with (sign out block) i know this will made with session but i cant do it so i need some help.....\[code\] <div class="sidebar"><!-- ---------------------------------------------------------------------------------------- --> <!-- Begin Sign in block --> <div class="art-Block"> <div class="art-Block-tl"></div> <div class="art-Block-tr"></div> <div class="art-Block-bl"></div> <div class="art-Block-br"></div> <div class="art-Block-tc"></div> <div class="art-Block-bc"></div> <div class="art-Block-cl"></div> <div class="art-Block-cr"></div> <div class="art-Block-cc"></div> <div class="art-Block-body"> <div class="art-BlockHeader"> <div class="l"></div> <div class="r"></div> <div class="art-header-tag-icon"> <div class="t">Sign in</div> </div> </div><div class="art-BlockContent"> <div class="art-BlockContent-body"> <form action="login.php" method="post" > <table width="171" border="0" > <tr> <td width="97"> <input class="put" name="uname" type="text" size="10" /> </td> <td width="64" align="right" class="text_un">User Name</td> </tr> <tr> <td> <input type="password" size="10" name="password" /></td> <td align="right" class="text_pw">Pass Word</td> </tr> <tr> <td>&nbsp;</td> <td align="right" valign="top"><input class="button" type="submit" name="button" id="button" value="http://stackoverflow.com/questions/3799877/Sign in" /></td> </tr> </table> </form> </div> </div> </div> </div> <!-- End Sign in block --><!-- ---------------------------------------------------------------------------------------- --> <!-- Begin Sign Out Block --> <div class="art-Block"> <div class="art-Block-tl"></div> <div class="art-Block-tr"></div> <div class="art-Block-bl"></div> <div class="art-Block-br"></div> <div class="art-Block-tc"></div> <div class="art-Block-bc"></div> <div class="art-Block-cl"></div> <div class="art-Block-cr"></div> <div class="art-Block-cc"></div> <div class="art-Block-body"> <div class="art-BlockHeader"> <div class="l"></div> <div class="r"></div> <div class="art-header-tag-icon"> <div class="t">Sign out </div> </div> </div><div class="art-BlockContent"> <div class="art-BlockContent-body"> <form action="login.php" method="post" > <table width="171" border="0" > <tr> <td>&nbsp;</td> <td align="right" valign="top"><input class="button" type="submit" name="button" id="button" value="http://stackoverflow.com/questions/3799877/Sign Out" /></td> </tr> </table> </form> </div> </div> </div> </div> <!-- End Sign Out Block --> </div> </div>\[/code\]