One item which is important is the monitor. There is a relation between clock speed and the raw power of your computer, but it is not a one to one relationship. More than likely, the person at the store was just trying to stun you with numbers. That really depends on what you plan to save on your computer. In fact, the majority of the hard drive is empty.
Storage memory continues to drop in price.
These days most PCs come with at least a 6 GB hard drive as the standard. Here at the university, you can store some of your data on a Network drive. To accommodate non-Western text, there is a system which uses two bytes to store a character. If we were talking about almost anything other than computers, a GigaByte would be 1,000,000,000 bytes.