I use root explorer, but you can also use adb pull and push.
RootExplorer Method
go to /system/bin/
open in text editor - mount_ext3.sh
add the following lines to the very bottom
chmod 4755 /system/bin/su
chmod 4755 /system/xbin/su
chmod 755 /system/app/Superuser.apk
ADB method
adb pull /system/bin/mount_ext3.sh
open the file in your favorite text editor
add the following lines to the very bottom
chmod 4755 /system/bin/su
chmod 4755 /system/xbin/su
chmod 755 /system/app/Superuser.apk
adb remount
adb push mount_ext3.sh /system/bin
adb shell "chmod 777 /system/bin/mount_ext3.sh"
Done!!!
This method was proposed by Djrbliss, and only slightly altered by P3droid...please thank @DjrBliss on Twitter as well as P3Droid.