Below is something I once did with the net group command to add bulk users to a security group. You can use the same concept using the 'net user' command or the 'dsadd user' command. Just set up your Excel spread sheet with the proper arguments. I would suggests getting into VBSCRIPT or PowerShell when you get the time, for now this still works great.
U can use the net group command to do this.
Using your Excel Spread sheet place these in the following columns:
A - NET GROUP
B - "group name" - the name of the security group
C - SAM Account of the user. Just copy from the 1500 you have.
D - /ADD
Your excel spread sheet should have 1500 entries similar to this:
NET GROUP FILESHAREREAD jdoe /ADD
NET GROUP FILESHAREREAD tlin /ADD
NET GROUP FILESHAREREAD ltom /ADD
and so on...
Next save your Excel spread sheet as a comma delimited .csv file. Open the file in wordpad or notepad. I prefer wordpad because it is multi-threaded which will be quiker in doing the next step.
From Wordpad, under the Edit menu, choose replace. In Find what: type in a comma (,). In the Replace with: type the space bar. Hit the Replace All button which will remove the "," and replace with " " (without the quotes of course).
The file should go from:
NET GROUP, FILESHAREREAD, jdoe, /ADD,
To:
NET GROUP FILESHAREREAD jdoe /ADD
For all 1500 entries (be patient).
Select All and Copy. Open a command prompt - right click paste. Away you go...
FYI: the NET GROUP command is required to be run on a domain controller.