pages navigation – child display

hi,

my navigation looks like this.

mainpage1 | mainpage2 | mainpage 3
childpage1 |childpage2

i use this for the mainpage navigation:
<?php wp_list_pages(‘exclude=6,7,8&title_li=&sort_column=menu_order&depth=1’); ?>

and this for child page navigation:
<?php wp_list_pages(“child_of=$post->ID&depth=1&title_li=”); ?>

two problems:
on the childpage i would like to keep the respective mainpage link highlighted, which the childpage belongs to.

2nd problem, on the childpage the childpage navigation disapears. has probpably something to do with the depth=1, could’nt figure it out yet.

thanks
dex