If you are going to work in Graphic Design or Web Design you are going to need a good computer. Now it is in no way a requirement to get a Mac computer and I’m not here to start the debate. It has been my experience, over 10 years making money in this business, that a mac computer is ideal for working with the adobe software. The font rendering is more crisp and real to what you will be seeing in print for example, also the font management software built into the operating system has its advantage. Just as Microsoft Word might hiccup when you are using it on a mac, I find that the Adobe Creative suite can be sluggish on a PC. Figure out what is best for your needs. I recommend a mac.
Now that said I’m also a very cheap person so I always buy refurbished. Go to the apple store and look in the footer of the page for the refurbished mac computers they will be cheaper. Even the bottom of the line is fast enough as long as you are not doing any video rendering. If you are doing animation or video rendering get a beefier computer.
A mac mini or macbook air will be sufficient. I have a 27 inch imac. I find this setup to be ideal. Find your work set up.