I suggest you BUILD a computer, if you are into gaming and things like that, but if you are just going to use a computer for personal use at home like designing, and music and stuff, you can probably just go to dell.com and customize a computer with a bigger hard drive, a better graphics card, and possibly a faster processor..
If you are into gaming, you should deff. build your own, but MOST good rigs cost up to $1500-2000.. I am currently building one that costs about $1k, and I am going to change around some parts soon, but I'm not exactly done yet (not to mention all the S+H and taxes would add up to be over 100 bucks)..
So, yeah build your own, but you should know what your doing or get someone who does to help you pick out the good parts and install them..
Always go for "the best bang for your buck", not just the latest and the greatest.. That stuff usually isn't necessary but some people get it simply because they have a lot of money to throw into a computer, unlike others..