Modify Sidebar ‘Pages’

Hi guys!
I want to change my sidebar on my blog: https://cessi.pytalhost.com/index.php
as u can see the section “Seiten” (=Pages) is quite long. is it possible to hide the subpage (e.g. Alex, Fuxi, Manu,…) as long as u are not on the specific page (in this case: “about us”)?!
i would appreciate every help!

ps: if u view my blog with internet explorer 6 some sites (e.g. https://cessi.pytalhost.com/wp-content/plugins/polls/wp-polls.php ) is not displayed correctly. why?!

greetings,
Oliver