que rom tienes! si tienes la 2.2 AOSP de serie es con z4root. Si tienes la ginger con superoneclick:
Get su-3.0-efgh-signed.zip from
http://androidsu.com/superuser copy Superuser.apk and su from the zip file to: \android-sdk\platform-tools\
Let the device connect and do this from the Windows commandline (\android-sdk\platform-tools\):
adb remount
adb shell "rm /system/app/superuser.apk"
adb push Superuser.apk /system/app
adb push su /system/bin
adb shell "chmod 6755 /system/bin/su"
adb shell "rm /system/xbin/su"
adb shell "ln -s /system/bin/su /system/xbin/su"
(remove the USB cable and turn device off and on again)
un saludo