I haven't tried it yet and I suspect Adobe wouldn't want you to, but you might try donwloading the updates to PS CS and pulling the ACR plug in off there. PS 7.0 shouldn't care whether the plug in is only for CS version or not. and the file can be moved around fairly easily (just make sure to keep your old one in a separate directory (or renamed) until confident the new one works or not).
If for some reason I need to use my old computer for photos that is one of the first things I would try as I can't load PS CS on it (Win98SE).
Just a thought, not sure if okay to do or not, youz takes youzz chances.