An ISO is a binary copy of a CD, including not only the data contained on it, but also information about the logical estructure of the data on the CD, as there are a couple different ways to store data on a disc. Simply put, is a clone of the cd in a file. The point of using an ISO with your problem is that hard drives are many times faster than optical (CD, DVD) drives. If your problem is caused by a slow data transfer rate between cd and computer (pretty common with psx cds), this will solve it. Another possibility to save some hd space is to use PEOPS cd plugin, and configure it properly (namely, use ictl scsi command interface, thread read method in a WinXP box).