FIRST YOU ARE GOING TO HAVE TO FIND A SPARE TARGET LINE (UNDER LINES) ONCE YOU HAVE DONE THAT YOU ASSIGN THE REC # TO THAT LINE THEN YOU HAVE TO ASSIGN THAT TARGET LINE TO THE SET (TERMINAL AND SETS. IF YOU DON'T HAVE ANY RECORDS FOR YOUR TARGET LINES THEY START WITH LINE 145 ON A MICS

If you have DID numbers in the system already it's actually pretty easy.  The incoming lines are numbered.  The Target lines come in, beginning at line 145.

What you will need:
1.  How many digits are being pulsed to your system?
2.  What is the phone set the DID is going to appear on?

1. Log into the system (Feature **266344)
2. You will see "Terminals&Sets"
3. Press the Next button to get to lines and when there press "Show"
4. Look for the lines beginning at 145.  When at line 145 press the "Show" button twice and then the "NEXT" button to get the Target line information.  (You should write these down and keep them somewhere, so you know who has what DID numbers
5. Go to the next available line.  You will know, because the Prime Set indicator will begin showing the Attd number.
6. At that open line you will enter the "Rec'd #".  This is what the LEC pluses you.
7. Next you will enter in the phone extension that the DID will route (if you don't know, go to the phone and press Feature * 0 and press the intercom key and it will tell you)
8. You should then just hit "next" until you are out of the Line information.  
9. Go back to the set information and make sure that whatever line you programmed as the Target line Rings on the actual phone set.

This is cavemanish typing, but it should work.

hope this helps