So, we're talking about a version of Minecraft newer than 1.5, which means that the game organizes its files slightly differently.
Seeing as you can have multiple "profiles" in the newer launcher, and that they can have different versions, one might ask: How might they manage all these different versions? It's actually quite simple if you think about it. Basically, the game uses a folder containing multiple other folders, each of these containing a .jar and dats file for a certain version of Minecraft.
First off, navigate to the AppData folder where the Minecraft files are located. Assuming you're running Windows 7, open the file browser and search for "%appdata%". The first result should be the right folder. Alternately, navigate to it manually by going to: "C:/Users/[your username]/AppData/Roaming". Note that AppData is a hidden folder, so enable "Show hidden folders" if you don't already have it enabled.
Your .minecraft folder should be located here; open it. There should be a folder labeled "versions", which is what we're going after. MINECRAFT SERVERS LIST Open it and look for a folder with the same name as the Minecraft version you are looking for; in your case, it will be named "1.7.4". Inside this folder should be the jar file you're looking for.