USE master
go

DECLARE @dbname sysname

SET @dbname = 'name of database you want to drop connections from'

DECLARE @spid int
SELECT @spid = min(spid) from master.dbo.sysprocesses where dbid = db_id(@dbname)
WHILE @spid IS NOT NULL
BEGIN
EXECUTE ('KILL ' + @spid)
SELECT @spid = min(spid) from master.dbo.sysprocesses where dbid = db_id(@dbname) AND spid > @spid
END

http://www.julian-kuiters.id.au/article.php/sql-server-2005-snippet-drop-db-conn

Drop all connections to a sql 2005 database

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