Why do you need the speed of a SATA HD for an enclosure? I use mine as means to rip huge amounts of data from other machines so USB 2.0 is easily good enough (10 meg a second IIRC).
If you have a fast HD it should be your C drive, can't really see that a fast enclosure would help, even if your machine could support it.
You can get add on PCI cards which support SATA but I don't know whether they would support it over USB or Firewire.