This is for Windows 2000 (may work as long as only your exe files got hosed)
Can you Use the run command? Try running cmd. If that doesn't work try typing command then press ok.
If you get the dos box (I saw your profile said you were running Windows 2000)
ren c:\winnt\regedit.exe regedit.com
Then try to run regedit.com.
Here is more on getting your default settings back. Also can be used (I think) if you can log on as a different user.