Alors un peu plus de détails, voila la procédure que j'ai suivi (anglais obligé

) :
A adapter en fonction de vos chemins sur votre mac ...
Here we go:
1) Insert your Leopard install DVD and reboot while *holding* the 'C' key until the gray Apple logo startup screen with the spinning loop appears. Choose a language when prompted, but do not continue with the install.
2) There's a menu bar at the top of the screen. Select the "Terminal" application.
3) Use the "change directory" (cd) command to make the system extensions directory your current working directory using the syntax below:
cd "/Volumes/Macintosh HD/System/Library/Extensions"
4) Use the "copy" (cp) command to copy the 10.5.6 kernel extensions that were backed-up into your current working directory using the syntax below (note the use of quotes and the space before the final dot):
cp -Rp "/Volumes/Macintosh HD/Users/[username]/path/to/Backup_IOUSBFamily_kext_10_5_6/"*.kext .
5) Change the user and group ownership of the kernel extensions to root and wheel respectively using the following syntax:
chown -R root:wheel AppleUSBHub.kext
chown -R root:wheel IOUSBCompositeDriver.kext
6) Change your current working directory to one level above the Extensions directory and move the "Extensions.mkext" file to your Desktop using the syntax below:
cd ..; mv Extensions.mkext "/Volumes/Macintosh HD/Users/[username]/Desktop"
You may notice the system immediately replace Extensions.mkext with a similarly named, zero-length file. Leave it alone.
7) Type "exit" at the Terminal prompt and use the pull-down menu to Quit the Terminal application.
8) Use the pull-down menus again to select the "Startup Disk" application and choose your normal startup disk (the one you've just been moving things around in above) and hit the "Restart" button.
Let the system boot as it normally would. If all went well, you will have now regained keyboard and mouse functionality.