EDIT: Please see my new version of this stored procedure.

I've been asked a few times if there was a way to change the number of days to retain the backup files for in my backup stored procedure.  Due to this, I have modified the sproc so that you can now input the number of days to retain the files for.  Here is the updated version:

----------------------------------------------------------------------------------------------------
-- OBJECT NAME         : isp_Backup
--
-- AUTHOR               : Tara Duggan
-- DATE     : December 18, 2003
--
-- INPUTS    : @Path - location of the backups
--        @dbType - which databases to backup - All, System, or User
--        @Retention - numbers of days to retain backups
-- OUTPUTS    : None
-- DEPENDENCIES         : None
--
-- DESCRIPTION         : This stored procedure performs a full backup on all of the user databases
--
-- EXAMPLES (optional)  : EXEC isp_Backup @Path = 'E:\MSSQL\Backup\', @dbType = 'All', @Retention = 5
----------------------------------------------------------------------------------------------------
CREATE            PROC isp_Backup
(@Path VARCHAR(100), @dbType VARCHAR(6), @Retention INT = 2)
AS

SET NOCOUNT ON

DECLARE @Now CHAR(14) -- current date in the form of yyyymmddhhmmss
DECLARE @DBName SYSNAME -- stores the database name that is currently being processed
DECLARE @cmd SYSNAME -- stores the dynamically created DOS command
DECLARE @Result INT -- stores the result of the dir DOS command
DECLARE @RowCnt INT -- stores @@ROWCOUNT
DECLARE @filename VARCHAR(200) -- stores the path and file name of the BAK file

CREATE TABLE #WhichDatabase
(
 dbName SYSNAME NOT NULL
)

-- Get the list of the databases to be backed up
IF @dbType = 'All'

 INSERT INTO #WhichDatabase (dbName)
 SELECT [name]
 FROM master.dbo.sysdatabases
 WHERE [name] <> 'tempdb' AND
    [name] NOT IN (SELECT database_name FROM msdb.dbo.log_shipping_databases)
 ORDER BY [name]

ELSE
BEGIN

 IF @dbType = 'System'

  INSERT INTO #WhichDatabase (dbName)
  SELECT [name]
  FROM master.dbo.sysdatabases
  WHERE [name] IN ('master', 'model', 'msdb')
  ORDER BY [name]

 ELSE
 BEGIN

  IF @dbType = 'User'

   INSERT INTO #WhichDatabase (dbName)
   SELECT [name]
   FROM master.dbo.sysdatabases
   WHERE [name] NOT IN ('master', 'model', 'msdb', 'tempdb') AND
      [name] NOT IN (SELECT database_name FROM msdb.dbo.log_shipping_databases)
   ORDER BY [name]

  ELSE
  BEGIN

   DROP TABLE #WhichDatabase

   RETURN -1

  END

 END

END

-- Get the database to be backed up
SELECT TOP 1 @DBName = dbName
FROM #WhichDatabase

SET @RowCnt = @@ROWCOUNT

-- Iterate throught the temp table until no more databases need to be backed up
WHILE @RowCnt <> 0
BEGIN

 -- Get the current date using style 120, remove all dashes, spaces, and colons
 SELECT @Now = REPLACE(REPLACE(REPLACE(CONVERT(VARCHAR(50), GETDATE(), 120), '-', ''), ' ', ''), ':', '')

 -- Build the .BAK path and file name
 SELECT @filename = @Path + @DBName + '\' + @DBName + '_' + @Now + '.BAK'
 
 -- Build the dir command that will check to see if the directory exists
 SELECT @cmd = 'dir ' + @Path + @DBName

 -- Run the dir command, put output of xp_cmdshell into @result
 EXEC @result = master.dbo.xp_cmdshell @cmd, NO_OUTPUT

 -- If the directory does not exist, we must create it
 IF @result <> 0
 BEGIN
  
  -- Build the mkdir command  
  SELECT @cmd = 'mkdir ' + @Path + @DBName

  -- Create the directory
  EXEC master.dbo.xp_cmdshell @cmd, NO_OUTPUT

 END
 -- The directory exists, so let's delete files older than two days
 ELSE
 BEGIN

  -- Stores the name of the file to be deleted
  DECLARE @WhichFile VARCHAR(1000)

  CREATE TABLE #DeleteOldFiles
  (
   DirInfo VARCHAR(7000)
  )

  -- Build the command that will list out all of the files in a directory
  SELECT @cmd = 'dir ' + @Path + @DBName + ' /OD'

  -- Run the dir command and put the results into a temp table
  INSERT INTO #DeleteOldFiles
  EXEC master.dbo.xp_cmdshell @cmd

  -- Delete all rows from the temp table except the ones that correspond to the files to be deleted
  DELETE
  FROM #DeleteOldFiles
  WHERE ISDATE(SUBSTRING(DirInfo, 1, 10)) = 0 OR DirInfo LIKE '%