Since you are using SQL Express you can't use SQL Server Agent. However there are many alternatives, all of which you can schedule using schtasks or Windows Task Scheduler depending on your operating system:
All of these languages/tools (and many others) have the capacity to connect to SQL Server and execute a stored procedure. You can also try these Agent replacements:
Here is an example using VBScript:
Open Notepad. Type the following code, replacing $tokens$ with your real values:
s = "$your server/instance name$"
db = "$your database name$"
u = "$your SQL auth user ID$"
p = "$your SQL auth password$"
constr = "provider=SQLOLEDB;Data Source=" & s & ";Initial Catalog=" & s & _
";User ID=" & u & ";Password=" & p & ";Network=DBMSSOCN;"
Set conn = CreateObject("ADODB.Connection")
conn.Open constr
conn.Execute "EXEC dbo.$your procedure name$;"
conn.close: set conn = nothing
Save this file as c:\somewhere\ScheduledProcedure.vbs
Open a command prompt and type the following (this will schedule this script to run on the 15th of every month at midnight), all on one line:
schtasks /create /tn "some name"
/tr "wscript ""c:\somewhere\ScheduledProcedure.vbs"""
/sc monthly /d 15 /st 00:00
To see this task in your list of scheduled tasks (there are a lot, but it should be in the very first group):
schtasks /query
If you later want to delete it:
schtasks /delete /tn "some name" /F