You are right, the notepad replacement can't be downloaded anymore, although it still works on my WinXP SP2 32-bit x86. I think, MS has something to do with the removal of this tool. I guess, MS does not like that one of their programs is replaced with a different EXE with the same name. Or some anti-virus program don't like it if they have CRC sums for original notepad.exe.
However, there are different methods to replace Notepad with UltraEdit. But before I post here any of them, I have one question.
Why do you need the Notepad replacement?
If you need it only because some file types are associated to be opened with Notepad and you want to open it with UltraEdit, then you can re-associate it with the File Associations configuration dialog of UltraEdit. UE remembers with which application a file type is currently associated and restores that when you later remove the file association of UltraEdit with the file with the File Associations configuration dialog of UltraEdit.
Well, for files like batch files which are opened with the command processor, but edited with Notepad, you need to modify the application for the Edit action in the Windows Explorer - Tools - Folder Options - File Types tab.
You can also use Regedit and search for every Notepad.exe and modify the value to uedit32.exe with correct path. But you should have experience with the registry when working with Regedit.
Best regards from an UC/UE/UES for Windows user from Austria