Yep it's backwards compatible with SATAI & SATAII. You will not get the advantage of SATAIII speeds, however. But you can use this drive in another device in the future that has SATAIII.
I highly recommend SSDs, especially for older Macs. It will give you significant boost in speed and bring new life to it. Even a 2006/2007/2008 model. Not sure of 2006 is pATA, though. Just make sure you at least have a SATAI connection in there.
Use System Information to see what SATA connection you have.
At $90 it's a steal. If you need more space, get a data doubler and replace your DVD drive with your HD that you have already and use it as a storage device 🙂