I'm having exactly the same problem as Steevo and Pandero, but I'm on Windows XP SP3, using Firefox 3.0.5. On Mission 7 and 9, the Remington M24 SWS cannot hit the satelite dish, or anything else for that matter - I fired over 25 rounds into various parts of it to no effect, and it also is unable of shooting through the window, the tv, etc. The only fail condition you can reach is running out of ammo. With the .308 Winchester I had no problems. I saw the same problem on Mission 9. I can fire as many shots as I want and no one is alarmed, etc.
My exact equipment in mission 7 and 9 (in case its a combination) was the Remington M24, the 4-12x40 scope, the rifle sling and the bipod.
Other than those glitches, I like the game, although the plethora of typos in the mission briefings are a little sloppy.