Indexing URL's in SQL Server 2005

CREATE FUNCTION GetUrlId (@Url nvarchar(400))
RETURNS int
AS BEGIN
  DECLARE @UrlId int
  SELECT @UrlId = Id FROM Url WHERE Url = @Url
  RETURN @UrlId
END

INSERT INTO
  UrlHistory(UrlId, Visited, RemoteIp)
VALUES
  (dbo.GetUrlId('http://www.stackoverflow.com/'), @Visited, @RemoteIp)

stackoverflow.com      -> com.stackoverflow
blog.stackoverflow.com -> com.stackoverflow.blog