There is only so much you can do with this old machine... you can install a SATA II controller but you'll still be limited to the speed of the PCI bus of 133mb a second so effectively ATA133.
You could install a SATA SSD on a PCI card but its transfer rate will be limited to 133mb/s.
You can not have Thunderbolt in these machines and even if you could it would also be limited to 133mb/s because of the PCI bus.
To be honest, you're better off just getting a faster machine.