i coudn't get it what i understood u want to search for a file named with config_mp.cgf
in mw2 folder and find in it's text r_fullscreen "0" and replace it with r_fullscreen "1" then save it is't right?
if so
Dim S As String = Nothing
Dim Mw2Config_mpcfgLocation As String = Nothing 'replace nothing with the location of config_mp.cfg
S = My.Computer.FileSystem.ReadAllText(Mw2Config_mpcfg Location)
S = S.Replace("0", "1")
System.IO.File.WriteAllText(Mw2Config_mpcfgLocatio n, S)
this get all text of config_***.cgf to s declared string then it replaces 0 in it with one
if i'm wrong please tell me what you want