Accesing to sharepoint web services anonymously from Silverlight

I'm working in a MOSS 2007 public website, anonymous access is turned on, using Windows Authentication, and I've a Silverlight app that uses information from a public sharepoint list.

I'm invoking the Lists.asmx web service

The problem is that I'm always prompted for login when I call to the web service...

I cannot create Credentials because of Silverlight...

Could you help me?

Thank you!