Update: Snapshot 13w37b has been released. You can select these versions in your launcher, or download the server links below.
To get snapshots, open your launcher and press the “New Profile” button. Call it “snapshots” and check the box saying “Enable experimental development snapshots” and save. To switch to the normal version, you can select it in the dropdown at the bottom left corner of the launcher.
Download Minecraft 1.7: Snapshot 13w37b: