HDD designs have moved on. The original SATA has a 1.5 Gb/s max data transfer rate, but the new SATA II run at 3.0. New ones are completely backwards compatible if your mobo does not handle SATA II. In fact, most new HDD's arrive with a tiny jumper installed on a pin block to limit them to 1.5 Gb/s for this purpose - if you need 3.0, you have to remove the jumper.
As you've already seen, SATA is not the same as ATA, and they need different power supply and data cables. An OEM HDD will NOT have these, but they can be bought separately. Most Retail packaged HDD's will have the cables included, but check that detail to be sure when ordering. On the power supply side you MAY have an unused connector already; if not, the cable you get is a converter - it connects to a 4-pin Molex on one end and provides the SATA connector.
By the way, does your mobo have an open SATA connnector for your new drive to hook up to?