from droid wiki
Unlike any phone with an unlocked boot loader, custom recovery cannot be installed instead of the stock recovery. The only way to run it is by hijacking the boot process (for stock ROMs) or providing an option in the bootup process of a custom 2nd init-based ROM.
To install CWM on a stock Droid device, you need to:
Root the device
Install Droid 2 Recovery Bootstrap
Open Droid 2 Bootstrap Recovery
Press Bootstrap Recovery; the application should pop up a message about a successful installation
Get ROM Manager
from the Market.
Start it, and choose the first item, Flash ClockworkMod Recovery.
Choose DROID X (2nd-init) (this is important).
Grant Superuser privileges when asked to.