iTunes does not read any ID3v2 tag for ratings. iTunes stores rating information in the iTunes Library database and nowhere else.
That said, did you use the POPM tag for the rating?
If so, I wrote a script that reads the MP3's POPM tag (which is a decimal value from 0 to 255) and translates that to an iTunes rating ( a value from 0 to 100).
Download the (free) program here:
http://home.comcast.net/~teridon73/itunesscripts/
Select the tracks in iTunes that you want to import the rating from. If you want to just test it out, select only one or two tracks.
Extract the zip and run "teridons
itunesscripts.exe". In the new window that appears, select "mm
rating_toitunes" and "Run selected script".
Again, you have to select the tracks in iTunes before you run the script.
NOTE: If the track already has an iTunes rating, it will be overwritten with whatever the POPM tag has.
I may receive financial compensation from my link (there is a PayPal donation button in my program).