System.Net.CredentialCache not found

Hi,

i need to do a HttpWebRequest against a SharePoint 2007 Server with NTLM Authentification.
For this purpose i need to use the CredentialCache in Systen.Net namespace.

VisualStudio says "The type or namespace name 'CredentialCache could not be found...".
But HttpWebRequest Class is found in this namespace.

Is this an error? Is there an alternative for doing a WebRequest with NTLM Authentification?

Thanks!