If you are wanting to backup your system without ANY monetary investment, it's not likely going to happem.
You will either need to purchase more disk and/or some backup software.
If you have and extra server available, you can use FTP to send over files to back them up.
With the cost of backup services these days, I would investigate them. Not only do you get the data backed up, but it is automatic and you do not have to worry about it.
Carbonite seems to have a good reputation.
The Q is about to free / without use 3rd party SW to back up Windows 7 ! Okay....
Windows 7 has an integrated backup solution which can be found Control Panel. Of course, prior versions of Windows also has backup utility, but now it is more improved in Windows 7.
U may invoke Backup And Restore from Control Panel or by typing Backup in the Search box on the Start menu. It is possible to take back up files to a local hard disk / a removable disk (like cd or dvd) / another computer on the network.
By doing open Control Panel > System and Security > Backup your computer option. On left pane, open the link “Create an image backup”.
Though the above procedure is very much sure and completely ok, u may also download and use for more enhancement and they r all completely free to download & use.....
<a href="http:// http://backup.comodo.com">Comodo BackUp</a>
<a href="http://www.qpointsoft.com/download.php">TrueSafe Personal Edition</a>
Don't worry, they r all free to use !
Remember, if u have more money u may invest it to get better solution. Though u asked for without purchase any sw, i.e. free, that is why I am providing these. It is universally known that, if u provide money for any good purpose, u should get always better way even a best option.