To change the name of the Start button:

Copy EXPLORER.EXE in your Windows directory to another directory
Start a hex editor (I've been using Diskedit from Norton)
Edit EXPLORER.EXE
Search for the string 53 00 74 00 61 00 72 00 74
This is the word Start with the letters separated by a null character
The section you are in should also have the words "There was an internal error..." also separated with the null character immediately following
Now just replace the Start letters with any of your choice (up to 5 characters only)
Exit Windows
Boot to DOS
Copy your new Explorer file over the original
To change the Start button icon:

Copy USER.EXE in your \WINDOWS\SYSTEM directory to another directory
Use an icon editor that can replace icons in executable files
Edit USER.EXE and replace the flag icons with the icon of your choice
Boot to DOS
Copy the new USER.EXE
The same can be done with NT 4.0, just the offset will be different but the location to just before "There was an internal error..." is the same.