When trying to get Greek characters to work on IIS7.5 on windows server 2008 I initially thought it would be tricky. In the end is was as simple as running the following command in an elevated command prompt
reg add HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\w3svc\Parameters /v FastCGIUtf8ServerVariables /t REG_MULTI_SZ /d REQUEST_URI\0PATH_INFOAs soon as you get the "Operation Completed Successfully" message. Just run
iisreset