No, because ROM Manager doesn't work on the Milestone.
G.O.T. is simple.
1) Google G.O.T. OpenRecovery.
2) Download it.
3) Unzip it.
4) Put OpenRecovery folder and update.zip on your SD Card
5) Turn off your phone.
6) Hold down the camera button while powering your phone back on.
7) When you get a screen with a triangle with an exclamation mark inside, press CAMERA and VOLUME UP at the same time until a menu pops up.
8) Use your physical keyboards navigation pad to navigate to "apply update.zip from sdcard" should be the second thing on the menu.
9) Depending on the version of GOT OR you got (1.14 or 1.44) there will be an area where it says Nandroid or Backup.
For future reference, Google would've turned up much more detailed, and many, many more tutorials, all Open Recoveries are applied and entered the same way, excluding ClockWork.