Don't know if this has any direct bearing on your problem or not (seems unlikely, given that your page isn't showing at all), but PHP 4.1.2 has certainly been causing enough problems to be 'blacklisted' in [Unknown]'s
Common Questions for 1.5.x!
FWIW, my attempts to access some things that *should* be there according to the forum URL you provided have produced nothing but 403 errors:
http://www.ausfx.com/yabbse/YaBBHelp/index.htmlhttp://www.ausfx.com/yabbse/YaBBImages/home.gifBut none of that appears to be responsible for your problems, so I'm afraid I'll simply have to leave this one for someone else!

PS One last thing which might just be worth a mention is that, while IE says 'Cannot find server or DNS Error', Mozilla's producing an alert box with 'The document contains no data.'