Lightroom does not use the Camera Raw plug-in. Instead, Lightroom virtually is Camera Raw. In other words, Lightroom is another incarnation of Camera Raw, however not as a plug-in but as a stand-alone program (and with a lot of extra functionality, such as Import, Database, and Presentation). Lightroom 2.2's raw converter functionality is the same as ACR 5.2.
The Camera Raw plug-in (i. e. the Camera Raw.8bi file) is for Photoshop and Bridge, not for Lightroom. The latest Camera Raw plug-in version for Photoshop CS3 is ACR 4.6; the current for Photoshop CS4 is ACR 5.2.
So if you have Photoshop CS3 and Lightroom 2.2 then you're using ACR 4.6 via Photoshop and ACR 5.2 as the built-in raw-conversion engine of Lightroom 2.2. If you want Photoshop to use the same raw-conversion engine as Lightroom then you'll have to upgrade to Photoshop CS4 in order to be able to use the Camera Raw 5.x plug-in.