RAID 0 works as follows. If you have two hard drives, it "stripes" them so as they appear as a single hard drive. However, the data is stored across both. For example, when you write a file, it writes the first bit to one drive, the second bit to the second drive, the third bit to the first drive, and so on.
The advantage is that when you're reading, both drives work nearly simultaneously. Therefore, the data transfer rate is twice that for a single drive. Exactly twice if you use SCSI, slightly less than twice if you use IDE drives, since the IDE synchronization is not as precise.
If you have more than two drives, the theoretical data transfer rate is the number of drives times the rate for a single drive. However, IDE have significantly more trouble synchronizing more than two drives.
The disadvantage to RAID 0 is that if only one of your drives fails, you lose all data. Also, the drives are better be of the same size. If one is 30GB and the other one is 40GB, then only 30GB of the second one will be used, and the extra 10GB will be thrown out.
If you wanted a 60GB storage, it might have been better to buy two 30GB drives and set them in a RAID 0 configuration. Only slightly more expensive, the same total storage, about the same access speed, and twice the data transfer rate.
If you already have a 60GB drive, it's up to you to decide if you want to buy another one just to double the data transfer rate. After all, you might do just fine with what you have, depending on what you use your computer for. But you probably see already that a RAID 0 configuration with a single drive doesn't make sense.
Leo