- shutdown the phone
- hold down volume up + power
- Now you are in the standard recovery mode
- assuming you have 2.3 SDK installed with fastboot (Google around for that info..), now on terminal/windows or Windows cmd depending on OS type "fastboot devices" to check your device can be seem via USB
- assuming you device is seen via fastboot devices, now type "fastboot oem unlock"
- accept...and new bootloader is unlocked...
- now we need a custom recovery from clockworkmod or amon_ra, and we'll be good to go
This was the same for the Nexus One, except of course different way to get into recovery...