R – sharepoint explorer view

Example of using the WSS "Copy" Web service to upload a document to a library...

public static void UploadFile2007(string destinationUrl, byte[] fileData)
{
    // List of desination Urls, Just one in this example.
    string[] destinationUrls = { Uri.EscapeUriString(destinationUrl) };

    // Empty Field Information. This can be populated but not for this example.
    SharePoint2007CopyService.FieldInformation information = new 
        SharePoint2007CopyService.FieldInformation();
    SharePoint2007CopyService.FieldInformation[] info = { information };

    // To receive the result Xml.
    SharePoint2007CopyService.CopyResult[] result;

    // Create the Copy web service instance configured from the web.config file.
    SharePoint2007CopyService.CopySoapClient
    CopyService2007 = new CopySoapClient("CopySoap");
    CopyService2007.ClientCredentials.Windows.ClientCredential = 
        CredentialCache.DefaultNetworkCredentials;
    CopyService2007.ClientCredentials.Windows.AllowedImpersonationLevel = 
        System.Security.Principal.TokenImpersonationLevel.Delegation;

    CopyService2007.CopyIntoItems(destinationUrl, destinationUrls, info, fileData, out result);

    if (result[0].ErrorCode != SharePoint2007CopyService.CopyErrorCode.Success)
    {
        // ...
    }
}

Here's a video about using Forms Auth. with WSS3 and here are some samples. Basically, you use the login.aspx page in _layouts to collect credentials and cache them. You have to modify web.config to use the membership provider. More on that here.