I’ve just downladed Camera Raw 4.3.1 update for CS3 and the plugin isn’t being recognised by photoshop. I haven’t had the camera raw plugin previous to this. Any ideas?
You should have had ACR with CS3; I don’t remember where it goes, but it isn’t a plugin in the usual sense, at least I don’t think it is.
The most recent ACR for CS3 is 4.6 — but Adobe have a rather confusing numbering system. 4.6 is the last release for CS3; but your camera may use the converter labelled 4.4 or somesuch — meaning that additions between 4.4 and 4.6 relate to other camera models — newer ones.
You could try getting PS to search for updates, which it should find and download and install automatically.