First thing you need to create a CGI (Computer Generated Imagery) is to have a computer of course :) Historically Apple's Macintosh has been the most popular platform among 2D digital graphic artists due to large number of professional plug-ins and color management tools available for professional programs such as Adobe Photoshop. However in modern graphic world, there is really no clear choice anymore since both Mac and PC have evolved considerably and most of the plug-ins and equipments are available in both platforms.
Whether your computer says Apple or Intel (or whatever), general rule is "faster the better". No brainer there : But more important than the power of processor is the RAM.

RAM (Random Access Memory) is the single most important factor in digital imagery. You can never have enough RAM. In the old Mac-rule days, typically, if you have RAM 3 times the image you usually work in, then you were in a good hand. However nowadays, that's not nearly enough if you use a lot of layers and channels. Does that mean if you have less memory, then it's impossible to work in the Photoshop? No, it just means it will be very painfully slow to work on CG. One great thing though is that the price of RAM has gone down considerably over the past several years. Nowadays, even GIGABYTES of RAM is affordable :D