Install ClockworkMod Recovery on Nexus One Manually
Step 1: Download ClockworkMod Recovery: recovery-clockwork-18.104.22.168-passion.img (there are more current, look at the xda)
Step 2: Set up ADB for Nexus One
Step 3: Put the downloaded recovery-clockwork-22.214.171.124-passion.img in C: drive
Step 4: Turn Nexus One off and connect it to PC via USB
Step 5: Hold the Power button + Trackball together to start Nexus One in fastboot mode
Step 6: Once in fastboot mode, open Terminal / Command Prompt and run following command:
This command will check if your device is connected in fastboot mode or not.
Step 7: Now run following command (place the file recovery in the same folder where the fastboot):
fastboot flash recovery recovery-clockwork-126.96.36.199-passion.img
This will install Clockwork recovery on your Nexus One.
Thatís it, enjoy!