AFAIK, there is no option to set tile sizes directly from the command line.

However, you could use the [python api][1] to do this, and execute a python script in blender from the command line. (see [this question][2])

To set tile sizes from python, you can use  
[`bpy.context.scene.render.tile_x`][3]
and [`bpy.context.scene.render.tile_y`][4].

Tile order can be set with `bpy.data.scenes["Scene"].cycles.tile_order`.  
This can be set to `'CENTER', 'RIGHT_TO_LEFT', 'LEFT_TO_RIGHT', 'TOP_TO_BOTTOM',` or `'BOTTOM_TO_TOP'`

An example script to set the tile size to 32x32 and set the order to `Right to Left`:

    import bpy
    
    for scene in bpy.data.scenes:
        scene.render.tile_x = 32
        scene.render.tile_y = 32
        scene.cycles.tile_order = 'RIGHT_TO_LEFT'
Note that it loops through each scene to set these properties globally. (see [this][5])  
You can run this from the command line with

    blender --background /path/to/my.blend --python /path/to/script.py --render-anim
    # or the short version:
    blender -b /path/to/my.blend -P /path/to/script.py -a

Borders:
==
AFAIK, it's not possible to tell blender to only render n amount of tiles, when n is less than the total tiles needed to render the complete image.
(blender does print a new line to stdout for every tile that is rendered, so you might be able to make some hack to stop blender once n tiles have been rendered, but I don't know if you could save output.)

Because of this, you might be better off using the [*Render Border*][6]; this will allow you to exactly define what section of the image to render.   
You could then call blender to render repeatedly, using a script to pass different render border dimensions to do your own "tile render".

You can enable border with `bpy.data.scenes["Scene"].render.use_border = True`

The border region is defined by four values between `0` and `1` corresponding to the locations of the four sides of the render border relative to the camera where `0` is the left or bottom edge of the camera, and `1` is the right or top edge.

You can set the [min and max xy values for the *camera* border][7] with

    bpy.data.scenes["Scene"].render.border_max_x
    bpy.data.scenes["Scene"].render.border_min_x
    bpy.data.scenes["Scene"].render.border_max_y
    bpy.data.scenes["Scene"].render.border_min_y

You may also want to enable *Crop to border* with `bpy.data.scenes["Scene"].render.use_crop_to_border = True`

So to render half of the image vertically, you could run this:

    import bpy
    
    for scene in bpy.data.scenes:
    
        scene.render.use_border = True
        scene.render.use_crop_to_border = True
        #this sets the render border to the left half of the camera. 
        #to render the right half, set max_x to 1 and min_x to .5
        scene.render.border_max_x = .5
        scene.render.border_min_x = 0
        scene.render.border_min_y = 0
        scene.render.border_max_y = 1
        scene.render.tile_x = 32
        scene.render.tile_y = 32
    #then render:
    bpy.ops.render.render()

Note that to set the *viewport* border you must use [this][8] instead, but you most likely are interested in camera border as viewport border is only relevant for using the realtime rendering feature. (see [this post][9] for more info)

Seeds:
==
This does not answer your question about tiles, but as you mentioned you want to do this for rendering on multiple machines, I thought I would mention this.

You could also combine different Cycles renders by using the [Seed][10] value. (See [this post][11] for more info)

This also is a good way to remove [fireflies][12].


  [1]: http://www.blender.org/documentation/blender_python_api_2_68_5/contents.html
  [2]: https://blender.stackexchange.com/questions/1365/how-can-i-run-blender-from-command-line-or-a-python-script-without-opening-a-gui
  [3]: http://www.blender.org/documentation/blender_python_api_2_68_5/bpy.types.RenderSettings.html?highlight=tile#bpy.types.RenderSettings.tile_x
  [4]: http://www.blender.org/documentation/blender_python_api_2_68_5/bpy.types.RenderSettings.html?highlight=tile#bpy.types.RenderSettings.tile_y
  [5]: https://blender.stackexchange.com/a/3062/599
  [6]: http://wiki.blender.org/index.php/Doc:2.6/Manual/Render/Output#Dimensions
  [7]: http://www.blender.org/documentation/blender_python_api_2_68_5/bpy.types.RenderSettings.html?highlight=border_max_x#bpy.types.RenderSettings.border_max_x
  [8]: http://www.blender.org/documentation/blender_python_api_2_68_5/bpy.ops.view3d.html?highlight=border#bpy.ops.view3d.render_border
  [9]: https://blender.stackexchange.com/a/2023/599
  [10]: http://wiki.blender.org/index.php/Doc:2.6/Manual/Render/Cycles/Integrator#Scene_Settings
  [11]: https://blender.stackexchange.com/a/998/599
  [12]: https://blender.stackexchange.com/questions/2275/what-is-the-reason-cycles-creates-incorrectly-colored-firefly-artifact-pixels