so what exactly does that mean?You cannot put a Droid ROM on a Milestone. They're too different. However...
CyanogenMod 6.1.0 RC4 for Milestone | android.doshaska.net
If you read the thread I just posted you will see that the alltel milestone is just a cdma Droid, not the GSM version w/ locked bootloader
So that means you should be able to root easily and load BB 0.5 or any other ROM for the droid. Just don't mess with the baseband(radio file).
Try z4root like FBM suggested. then download Rom Manager, flash clockwork recovery, make a backup, and start having fun.
If you can't find instructions for something PM me and I'll try and help.