I can't understand why it wouldn't work if you type in the address manually, it's almost like it's not sending the ?act=gettopic&topic=23 and instead it just goes to the index.
I don't have much experience with forum coding and this one isn't a widely used one such as phpBB or IPB.
Ok, I looked through the WolTab site and I searched through documents and other help files. Unfortunately, I couldn't find any mention of complete incompatability with IE. But, the current version of Burning Board is 2.3.2, this means that your version if very old and I think that there must have been a problem with it when it was released.
I also went into the WolTab forum(which is in German) and searched for explorer(after translating into German:Forscher) but that didn't yield any results.
My advice therefore is either:
[-] Get a different (and better) forum like IPB(recommended), or
[-] Get a newer version of Burning Board which should fix the problem
[-] Make sure everyone who uses your site doesn't use IE(not very practical)
Anyway, hope I helped some there, there doesn't seem to be a way to fix it other than replacing the forum.