I can't tell you for sure, but it should be easy to find it out.
I assume that you will buy a 9,5mm-HDD (320GB) if 12,5mm will not fit. So you should already have the HDD-case or you will order it anyway.
First take a foot rule and make a measurement.
If this seems to be ok, use a model. Take your first HDD and some paperboard (to reach the 12,5mm) and put it into the secondary slot.
The additional height is "on top" of the HDD, not "on the bottom" (relative to the interface) as far as I know.
If this fits, you know if the Hitachi will fit.
Please post the result!
If you need the 500GB (actually 465GB) and 12,5mm do not fit, then look for Samsungs Spinpoint M6. It has only 9,5mm and is anounced to be available from june.
But you will have to accept a lower shock resistance (750g/325g instead of 1000g/400g) since it has 3 platters while other 9,5mm-drives only use 2 platters.
Edit:
Seems like the Samsung is already avalable in france:
http://www.engadget.com/2008/05/06/samsung-spinpoint-m6-500gb-laptop-drive-finally-on-sale-in-fr/