If u have recovery.img file then place it under the /sdcard directory like : /sdcard/recovery.img
Now goto terminal emulator & type:
flash_image recoveryonly /sdcard/recovery.img
wait for a while until new line is displayed. Now u should have a new recovery.
Switch off ur phone & press & hold Home & Power
buttons together to check if it's installed properly. In case u can't access new recovery, then normally switch on the phone(yes u can still switch it on...) & repeat the above procedure again in terminal emulator & now it will definitely work.
For me it took two tries to get it
Hope this helps...!!