I did worked out a temporary solution to login problems with IE7 and IE8:

Make a htaccess file and let it direct to http://www.domain.com/forums/ubbthreads.php if the url not containing 'www.domain.com'

Code
rewriteengine on
rewritecond %{http_host} !^www\.domain\.com$ 
rewriterule ^(.*)$ http://www.domain.com/forums/ubbthreads.php [r=301]

trosfrihed.dk
Custom Ubb 7.5.2