Doing this on my mac with terminal. Following this link...for the splash screen
My code that i should be typing in is this right?
./fastboot-mac flash splash1 splash1.nb
sending 'splash1' (750 KB)... OKAY writing 'splash1'... FAILED (remote: not allowed)
1) Your phone isn't S-OFF
2) You do not have the correct HBOOT version (which in your case, should be 0.76)
To check if these things are your problem, you need to boot into bootloader; and while booted, looked at the printed green text at the top of the screen; you should see both S-OFF and Hboot 0.76; if you do not, then those are the things you'll need to fix. If you have one thing right, but not the other; then that other thing needs to be fixed.
To fix the S-OFF issue, you'll have to install Unrevoked Forever on your phone. You must be ROOTED first though.
To fix the Hboot version (that is, to get 0.76) on your phone, you'll need to download the file that's inside this thread. But, in order to flash this file, you HAVE to be S-OFF, so do the above step FIRST -- if it's not done already
Good luck. Reply back if you need more help.