No custom recoveries available for prevail yet, as far as i know. but you can use Boot Animation Changer Lite from Market. There is an option to import your own bootanimation but you have to pay. BUT you can bypass this by using the option to restore default BA. Go to advanced and save default animation. Now, using whatever file explorer u have installed, go to /sdcard/bootanimStock/. Replace the bootanimation.zip with your own. Now go back to BACL - Advanced. Use the restore default animation. That should do it. I didn't try it out, but if you can't figure out what I described or just too lazy to do all the extra steps, there are animations and a option to switch animations included with app.
If you haven't yet, and are planning to try out ShabbyMod or a custom theme like Simple Green, you can replace bootanimation.zip that are included with them and kill 2 birds with one stone.