Just want to reiterate that the suggestion to delete (or rename) /system/boot-from-recovery.p would also work and enable you to keep your stock image yet get into CWM recovery.
If you don't want to spend the $4 for File Explorer, you can do what I did.
Download the following two apps:
Mount /system (rw/ro)
ASTRO File Manager
Start Mount /system (rw/ro) to put mount /system as rw
Navigate to /system folder via ASTRO and delte boot-from-recovery.p
Then go back into the first app to unmount /system
Done. OK to uninstall both apps if you don't need them. Also, the above file serves NO purpose except to block you from accessing a custom recovery, so don't even bother renaming, just delete and be done with it.