Need help with a “smart” navigation bar.

I am trying to make a “smart” navigation-thing for the sidebar (look here for visual). Well, maybe it wasn’t so smart since I havent managed to make it yet.

If viewing a single post i would like to retrive the url’s with “next_post()” and if on the frontpage i would use the “posts_nav_link()” function.

<div id="navcontainer">
<ul id="navlist">
<li id="navprev"><a href="## help me here ##">Previous</a></li>
<li id="navnext"><a href="## and here ##">Next</a></li>
</ul>
</div>

All i want to retrieve is the url of the next post (or page)… Is there any simple way to do this?

[edit]I am sorry this post ended up in the wrong section, still need the help though!