Just download "Z4ROOT" and put it on your sd card (at the root).
Then browse your sd card and install the app using a file explorer (ES File Explorer, Astro...).
Once the app's installed, make sure the debug mode is on (parameters>applications>development>usb debugging) and launch the app.
Choose between "temporary root" or "permanent root", let your phone reboot, then launch the app again and you'll see a superuser request... choose "Allow".
Your phone is rooted.
If you want, you can unroot by just launching this app again and choosing un-root."
Translated from Piticoeur topic on a french forum.