You're limited in what you can do with something this old (due to bus issues), and furthermore, you don't need SATA III for ordinary hard drives. That is why I suggested a two-port card, which will easily accommodate an SSD.
For an example of the benefits to be had, an SSD installed in a G41 Q9300 homebuilt that was moved from onboard SATA II to a PCIe-x1 SATA III card had its Windows Experience Index primary hard drive increase from 6.8 to 7.4. In comparison, an ASRock AMD 945 quad-core homebuilt has a 7.8 for that score and an XPS 8500 3570K has the full 7.9.