This is very quick and basic instructions
It appears that with WindowsME, only the boot screen can be replaced. Microsoft changed the "Please Wait..." and "It Is Now Safe...", for some reason..
The file is by default called either LOGO1.SYS, LOGO2.SYS, LOGO3.SYS
Click on the boot screen image that you want - you will be prompted to open or save the file logox.sys
If you are not prompted, right-click on the small boot screen image of your choice, then choose SAVE TARGET AS or SAVE LINK.
Decide which image you wish to replace based on the instructions below:
A) To use as the Windows 95 / 98 / ME startup screen, save this file to the ROOT of your C drive (C:\logo.sys)
B) To use this file as the PLEASE WAIT WHILE WINDOWS SHUTS DOWN screen, rename the file LOGOW.SYS and save in to your WINDOWS directory (C:\Windows\logow.sys)
C) To use this file as the IT IS NOW SAFE TO TURN OFF YOUR COMPUTER screen, rename the file LOGOS.SYS and save in to your WINDOWS directory (C:\Windows\logos.sys)