Update: I was unfortunately not aware of Shamus Young's severe criticism of Fallout 3 available here to link in the original piece and I regret that. It dovetails rather nicely with what I've written and it's much better executed than my piece. I strongly recommend anyone...
Mixed with explosive action, Call of Duty 4: Modern Warfare also delivers amazing special effects, including use of depth of field, rim-lighting, character self-shadowing, real time post-processing, texture streaming as well as physics-enabled effects to enlist players into the most photo-realistic gaming experience. Combined with Call of Duty’s award-winning audio design, players will face war as never before.
Frontlines will bring 3 brand new gametypes to Call of Duty 4 : Modern Warfare, plus a smart spawn protection to avoid the spawn killing that is happening in all COD4 servers around the world. Also have nice features from the common ones until few never made before. And before you ask... NO! will not have a HER version inclued in Frontlines, the game already come with HER from the store, it's the Hardcore mode.
Just create a subfolder under the 'Mod' folder in your Call of Duty 4 game folder and call it "zombie" (lower case) so that your path looks like this: C:Program FilesActivisionCoD4Modzombie
Then extract the contents of the zip file in to the newly created zombie folder. Done!