I was successfully running the trial version of Photoshop Elements 7 with 5.4 of the raw file filter. I purchased the Premiere/Photoshop Elements 7 bundle, uninstalled the trial, and installed both full versions.
I also downloaded Camera Raw 5.5 and installed it.
With 5.5 I would receive "Adobe Photoshop Elements (editor) has stopped working" when opening a Nikon NEF file, and Elements would abort. Both x64 and x32 versions of the Camera_raw.8bi file would cause the same problem.
I reinstalled 5.4 and it worked fine.
Windows Vista Ultimate x64 Service Pack 1
Inten Core2 Quad Q6600
Are you sure that you only have one copy of the plug-in installed in the install directory at a time?