Knowledgebase

See: http://blog.sharepointhosting.com/Lists/Posts/Post.aspx?ID=93

Go to Control Panel
Go to Internet Options
Click the “Security” tab
Click “Local Intranet”
Click “Sites”
Click “Advanced”
Add your SharePoint site into the “Local Intranet” zone.
Click OK to confirm on all Internet Options screens.
Open up Internet Explorer and go to your SharePoint site.  When prompted for username/password make sure you enter your credentials and check “Remember My Password”.
Your username/password should now be passed to the SharePoint site automatically.