The specs clearly say it has two IDE ports supporting up to 4 ATA100 devices, but no mention of SATA. How many are in there already? Space to connect one more? Review how to set Master and Slave jumpers and connect data ribbon cables. Make sure you check whether this board's BIOS supports "48-bit LBA" necessary to use HDD's over 137 GB.
Be aware I believe Abit got out of the mobo business, although they are still operating in many other products and their website for support works. Just not sure how much more support they can provide beyond the website.
Near as I can tell, there is no ATA 300 spec for hard drives. ATA 300 does show as a spec for air freight packaging. What you may have run into is "Serial ATA 300", which is another way of writing "SATA 300", also called "SATA II". This is the name for the second-generation version of SATA now in wide use (SATA 3 is just emerging), and NOT connected to any PATA (IDE) drive system.
So look closely - if the word "Serial" is before "ATA 300" they clearly are talking about SATA drives, not older IDE systems. And if it's not, read all the details carefully to be sure the unit is IDE, because the phrase "ATA 300" is not a common name for any drive type.
To get closer to your question, since your board has ONLY IDE (PATA) ports for hard drives, you will be looking for an IDE HDD type. And yes, they all had backwards compatibility. For example, an ATA133-capable drive certainly will work with your mobo's controller that supports up to ATA100. It even works the other way - an old ATA-66 drive would also work with your mobo, just slower.
If you buy a new drive you'll most likely get new cables, if not make sure you get 88 conductor cables or the drive will not operate higher than ATA33 no matter what speed it is capable of. On most drives you can leave your bios settings to auto and be alright. If your drive is larger than the bios supports you will get a dialog box on that.....