Trying To Get Exclusive Access To A DB For Restore.

I have created a SQL Agent job that is supposed to essentially duplicate a production database to another database. The code I am using is:

step1
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declare @sql varchar(8000)
set @sql=''
select @sql=@sql+'kill '+cast(spid as varchar)+char(13)+char(10)
from sysprocesses where dbid=12

--Print (@SQL)
exec(@sql)

step2
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RESTORE DATABASE HIWDYNARPT FROM PRDBACKUP
WITH REPLACE
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This works when I test it during the day, however when it runs at night I get the following error in the job log:

Database in use. The system administrator must have exclusive use of the database to run the restore operation. [SQLSTATE 42000] (Error 3101) Backup or restore operation terminating abnormally. [SQLSTATE 42000] (Error 3013). The step failed.

I'm not sure why this happens because I have killed all open threads in step 1, and then create my own new thread in step two. Maybe someone else is initiating a new thread to quickly between the steps???

Anyway, I am trying to use:
__________________________________________________ __
ALTER DATABASE HIWDYNARPT
RESTRICTED_USER
WITH ROLLBACK IMMEDIATE
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...as an alternative to the T-SQL killing PID's, but SQL 7.0 SP4 does not seem to support restricted user like 2000. It keeps giving me a syntax error. Does anyone have any suggestions?

If I bring step 1 and step 2 together, separated by "GO", could this fix the problem?

Thanks in advance!

Ryan Hunt