linker95 - I have recently see something in the Desire HD section that may be of some use to you...
Originally Posted by McCookie
I know you can replace the second bit by downloading a boot animation.zip of your liking and putting it here : internal memory/system/media . But I advise you to backup the original bootanimation.zip by either copying to your PC or renaming it to bootanimation.back
P.s. when you install a new ROM there will be a new startup screen anyway.
Let me know if this is helpful... I can always have a bit more of a look for you. As the user I have quoted says, if you install a new ROM, it should get rid of the carrier splash screen.