FileStream Write/Read

Question

Hi All,
can anybody tell me how to read or write Streamfield beginning from special line?

            FileStream fs = new FileStream("Specifications.txt", FileMode.Open);

            StreamReader sr = new StreamReader(fs);

            string SpecificationsModelSettings;

            SpecificationsModelSettings = sr.ReadLine(); ----> here I want to read beginning from Line "xxx"

I want to order datas in parts, and read/write only specific parts

thanx in advance