[support] Windows Logon ?

hi, I've setup a drupal 7.12 on a Debian squeeze box and I have a strange issue. I log on the drupal site with no problem with any browser on a linux and mac OS X box. But I can't log on with any browser on a windows os. Each time I enter the login / password, the system don't logon with no errors at all, Just displaying the home page again. Any ideas. Olivier.