Hello and welcome to SimV. May you have a great time with us

Firstly which version of Windows are you using?
I know with Vista one cannot make changes to the .CFG within root FSX folder.
You have one of 2 options:
1) You must disable the User Account Controll (UAC) which will enable you to add the required lines in the .CFG to make the textures appear.
The 2nd option is if you choose not to disable the UAC:
2) Copy the .CFG to your desktop, add the lines, save it and copy it back into the required folder.
Goodluck

Coolermaster Storm Enforcer Chassis/ Corsair TX750W PSU/ Gigabyte Ga-990fxa Mobo/ AMD Phenom X4 965 BE 3.4Ghz C3/Coolermaster V6GT CPU air cooler/ 8GB RAM Corsair DDR3 2000Mhz/ Gigabyte GTX570 Overclocked Edition GPU/ Windows 7 Prem 64bit/ 750Gb & 150