I have the preferences in CS3-Bridge and ACR set to open JPG & TIF files in ACR and not CS3 but when I click on a TIF file in bridge it opens in PS CS3 instead. These TIF files were generated by a GUI interface for ENFUSE which is an algorythm that combines bracketed RAW or JPG exposures for expanded dynamic range... it works very well ad outputs to TIF... but I can't seem to open these TIFs in ACR. Isn't a TIF a TIF?
There are many varieties of TIF files (including b/w fax images).
I have no idea if this will work, but you could try opening one of the files in Photoshop, saving as a TIF from Photoshop, and then see if that new TIF file will open in ACR. At least it should let you know of opening of TIF/JPG files in Camera Raw is working correctly.