Hi Christian, after checking the issue, it seems this is a general Windows XP issue. As this forum focuses on Windows Vista specific issues, this inquiry would best be posted to the following forum or support service:
http://forums.microsoft.com/TechNet/default.aspx?ForumGroupID=561&SiteID=17
http://support.microsoft.com/oas/default.aspx?ln=en-us&prid=11273&gprid=522131
The reason why we recommend posting appropriately is you will get the most qualified pool of respondents, and other partners who read the newsgroups regularly can either share their knowledge or learn from your interaction with us. Thank you for your understanding.
Also, I'd like to include the following KB article:
http://support.microsoft.com/kb/256614
Hope this helps!