I actually use the latest php-gtk (0.1.1a), but the problem seems to be the same with the latest PHP (4.0.6), both for win32. 

When we system() or fpassthru() (or same exec..) something which containts accents, it squizzes the accents and then 
make invalid the command.

for example : 

system ("cmd nul /c move \"C:\test\belenos-errances_oniriques\support_du_n?ant.jpg\"  \"C:\test\belenos-errances_oniriques\Support du N?ant.jpeg\"") ;

will be execute as :

move "C:\test\belenos-errances_oniriques\support_du_n,ant.jpg"  "C:\test\belenos-errances_oniriques\Support du N,ant.jpeg" ;

and so the file can't be found..