Browsing is a little tricky. You can "jump" to a given page within the forum by changing the value of the "start" field in the url (in your browser's location bar). Slinging.org displays 20 threads per page, so if you wan to go to page 27, you need to enter "start=520" the easiest way to to do this is just to click through to page 2, then edit the url (page 1 doesn't show the required fileds).
http://www.slinging.org/forum2/yabb/YaBB.cgi?board=admin;action=messageindex;sta...is page 2 of the admin area. Just change the 20 to how far into the listing you want to go and hit enter.
As for navigation, I use my browser's forward and back buttons. You won't see your read threads update until you reload the page - I tend to do this every few threads out of habit.
I'm pretty sure that there should be a url filed to let us bump the number of threads to disaply from 20 to some higher number, which would make life a little easier, but I haven't found it yet!
Matthias