I had to do this recently. My background is network and Win sys admin with limited dba skill.
What I found helpful was to install SQL Server 2005 Management Studio Express.
Once you've installed Mgmt Studio, pick the DB in question, right-click on the DB, choose All Tasks > Backup. Pick the right options for your case, and toward the middle on top is a button that says Script. Choose Script to File. Save to file and on the Backup window choose cancel (if you hit OK it'll run a backup, which may not be what you want at that time). This process will create a FileName.sql file for you.
Create a .bat file which for me looks like:
@ECHO off
ECHO Attempting to backup Database
sqlcmd -S localhost -E /i FileName.sql
ECHO.
ECHO If no error message is shown, then the database was backed up correctly.
ECHO.
PAUSE
Note: I placed the .bat and .sql in the same directory, hence the argument to /i is not absolute path.
Run the .bat file, and if there are no errors modify the batch file by removing the PAUSE.
Create a scheduled task to run the .bat file.