Unity should recognise it so long as windows does (not sure how well 360 controllers work with Macs). If you plug in your 360 controller (wired works best) and get windows to see it fine under Game Controllers, you should have no problems using it in a Unity Game. Make sure you use Input.GetAxis and Input.GetButton rather than Keys, and check your Project>Input Settings for default button assignments to the joystick.

Edit: Two additional points: although the 360 controller works as-is on Vista and later, you will need to get a driver for XP to see it, much like the PS3 SixAxis does.

The other thing is, I would not recommend getting direct joystick keycodes in Unity; far better to use GetButtonDown("Fire1"), as that will be called if the user pressed left mouse button, left CTRL or Fire 1 on the joystick (by default). The user can also re-map the keys when using GetButton and GetAxis. Have a look at the 3D Platformer tutorial, you should find that works with controllers straight away. Interestingly, though, I found I had to invert the Y axis when using a controller or else the stick forward-back motion was the wrong way around.

If you are using a Mac, or want to package a driver for mac, here is an open source driver.

Mac 360 Controller Driver

Also of note, check out Post on buttons mappings for a 360 controller

I tried it with a PS3 controller once. I had to:

• Find a driver so Windows can recognize the PS3 Controller
• Go to the GameController Settings in your Windows Systemsettings
• Calibrate your controller (it is useful to write down which button is assigned to which number)
• And use KeyCode.Joystick1Button0, KeyCode.Joystick1Button1, ... in Unity to get the Input.

This should help...

http://unifycommunity.com/wiki/index.php?title=Xbox360Controller

Setting up with the two joysticks on the xbox controller, one for forward/backward and sides, the right joystick for looking around: http://www.youtube.com/watch?v=Z591NmskYcY&feature=youtu.be