Compatible: It should be. SATA I, II, and III are, in theory, compatible. There have been problems running faster versions on SATA I controllers, which may not be fully forward-compatible.
Useful: If your interfaces are SATA I, you would get a bigger boost by buying a new rig with SATA II or III ports. Or installing an SATA III controller card. Stand by, I'm going to try to look up your specs... Can't find them.
So my answer is a resounding maybe