Hi ramya,
First Create one text file with below format for 1000 users.
Go to the User Administration-->Import.
Browse text file and upload it.
[User]
uid=
last_name=
accessibility=0
role=
group=
[User]
uid=
last_name=
accessibility=0
role=
group=
.........etc. Hope this will help you.
Regards
Narendar.