I've just downloaded Minecraft and I wanted to install Minecraft Forge, but it said I needed to go to bin folder than to minecraft.jar. I don't have minecraft.jar, only having versions, magic, launcher, launcher.pack.izma and launcher_profiles.json
The new Minecraft launcher and all versions that it supports exclusively (1.6 and up) have no bin folder/minecraft.jar. Also, it seems that Minecraft Forge has not yet been released for Minecraft 1.7.4.
When it does come out, you can either install mods the recommended new way using the new launcher, or you can directly edit the jar files.