my current mobo only has 2 SATA slots, i have 3x200gb hard drives. I'm wondering is there anyway i can connect the 3rd HDDs up to my PC? a SATA controller through the PCIe slots or something like that?
That's exactly what you need. You should purchase an external sata control card. They can be rather cheap depending on the brand name and everything - remember to buy what you think you will need in the future as well.
I actually don't have much experience with external controllers as I've only personally owned a highpoint ide raid card (not applicable), adaptec scsi (also not applicable) and a promise sata II 150 tx2plus (with 2 sata and 2 ide). The promise card wasn't terrible but it was hardly great at the same time - though I can't blame it for corrupting the hard drive that was on it since the card itself wasn't at fault (and neither was the hard drive.) The Promise also was somewhat slow to detect my hard drive sometimes after reset which was my only negative point about it. The last firmware they produced for tx2plus didn't solve the issue either - though they had ones for other controllers available. I wouldn't expect the same issue with the newer promise controllers. I also had a Siig sata controller in possession (but not mine) for 2 days but it worked fine during that time.
Make sure you get an internal sata one and not external or you'd have to loop it around. Apparently, this is one of the cheapest sata II controllers with two internal connectors. Handles RAID 0,1 but it's optional it seems. No clue on quality and long term performance nor any promises that it works with your system or is what you are looking for. http://www.newegg.com/Product/Product.asp?Item=N82E1681...