Old hard drives use the parallel ATA (IDE) technology which is restricted to transfer speed (U-ATA 33 is 33 MB per second and top transfer speed is U-ATA 100 or 100 MB per sec) and cable length (40 cm). Serial ATA is new and the transfer speed starts at 150 MB per sec and the cable length can be upto 1 meter. The form factor is also different: a thin flexible cable rather than the fatter ribbon cable.
Take a look at your Mobo, if you see a chip with SATA-link on it then your problem is that your SATA controller is using the PCI controller for indirect Drive control ( a bit like using a PCI SATA card). 66mb/s is about as fast as you can go. If your PC has a dedicated direct SATA controller, then you might have a first generation drive. Even the latest HDDs aren't much faster than thier Ultra ATA 133 counterparts, (they are basically the same, but with a Serial to SATA converter.)