1. open "Root Explorer". Accept any Superuser requests.
2. Navigate to where you downloaded the "bootanimation.zip" file. Copy (or cut) it.
3. Navigate as far up as you can into your root directory, and then Goto /system/media/, mount it in r/w mode.
4. Paste your "bootanimation.zip" file or replace it into /system/media/ (it must be named bootanimation.zip)
5. Change permissions as below. >>> rw- r-- r-- <<<
6. Reboot and enjoy!
Samsung Galaxy Y Young
Current Rom: my MiniJELLYBEAN
Samsung Galaxy S M110S
Current Rom: GFAN M110S FTE9K WF07 ODEX SP8
Samsung Galaxy S Captivate SGH-I897
Current Rom: C-RoM Mix v25