What colchiro said is pretty much self explanitory. If you're running stock, which is Gingerbread 2.3.3, and just rooted you would use an app called droid 2 bootstrap to get into clockwork recovery. You hit "clockwork recovery" then "reboot recovery" and you're in clockwork recovery.
If you're running MIUI, which is known as a 2nd init Rom, you have to download and install an app called terminal emulator. Start terminal emulator and type su. That will give you root access. Then you type cat.jpg. Close terminal emulator and start Rom Manager. Hit "reboot clockwork recovery".
Keep in mind you have to have clockwork recovery installed for whatever Rom you're running. So if you're running stock, or any Gingerbread Rom, you need to click "flash clockwork recovery" and select "droid X". Also keep in mind if you are stock you don't even need Rom Manager. Droid 2 bootstrap is all you really need. Some people just prefer to use Rom Manager anyway.
If you're running any 2nd init Rom you will click "flash clockwork recover" and select "droid X (2nd init). Then "reboot Recovery". Is this more helpful?