I searched winXP and found 2 instances of notepad.exe. The first is in C:\WINDOWS and the other is in C:\WINDOWS\system32, both identical files.
Did you remove both of them? if not, try using the one you didn't delete
Another way to get notepad back is by copying and expanding the file from your windows setup disk .
Put the windows XP disk into the drive, exit out of the autoplay setup menu.
Next, Search the disk for NOTEPAD.EX_, then copy NOTEPAD.EX_ to the C:\ drive (for easiest access).
After it is all copied, click start> then RUN. Type "CMD" to open the command line.
Next, type "cd C:\" (without quotes) to change the directory to C:\.
Finally, type "expand NOTEPAD.EX_ NOTEPAD.EXE"
Notepad should show up next to the NOTEPAD.EX_ file, and your able to use notepad again. Then you can copy the back to C:\WINDOWS and C:\WINDOWS\System32 as needed.