These days, most hard drives are of the ATA100 or ATA133 specification. The theoretical transfer rate of an ATA100 drive is 100 MBps; an ATA133 drive's theoretical transfer rate is 133 MBps. Of course, these are theoretical rates.
Many Linux systems use conservative defaults that could be slowing down your system. At the very least, these defaults could be preventing your system from reaching the maximum speeds that your hardware allows.
Like most parts of a Linux system, how Linux interacts with your IDE hard drives is configurable. You can accomplish this using the hdparm tool, which allows you to customize many aspects of any given IDE hard drive device.
Of course, using hdparm requires caution because your drive could end up corrupting data or failing if you configure it incorrectly.