Hi, I purchased my IS250 (my 2008) in Texas, brought it to Spain with me when I moved back.
Went to the Madrid Lexus dealer, purchased the OEM Disk and had the dealer exchange the US DVD for the European.
Lo and behold, it all worked fine (I was also 200 euros poorer)
Although some limitations (POIs wont show in the map), voice guidance works (in Spanish) and I am quite satisfied.
Cheers.
Diego