I am trying to find out how to use manual zoom. Can I connect the camera to my laptop and see the images on PC as I shoot them? I have a Canon 550D Rebel 2Ti.
Do I need any special cables for this?
The EOS Utility, via its Camera Settings/Remote Shooting module will let you Live View your pictures as you shoot them. It will also set you change the image settings (speed, aperture, ISO, etc.) via the PC. No special cable is required, just a regular mini-USB cable, which was supplied with your camera.
Note that for focusing purposes you don't really need this software, as live-view mode on the camera, together with maximum magnification of the live-view image should let you see your image at the pixel level (or close to that) so you can actually critically focus using your back LCD.
UPDATE: Just noticed you asked about manual zoom and not manual focus. In the EOS line, the lens zoom is always manual, and it has no relation to the EOS Utility. You can still use Live View mode on the camera to frame the photos if you find doing so via the viewfinder is hard.
There is free software that actually comes with your camera that can do this, its called EOS Utility, you can also download it from here.
In addition to that you can also use the Tethered shooting option in Lightroom 3