Local backup software? [duplicate]

Possible Duplicate:
What backup software for Windows?

I work in a corporate environment running Windows XP and I have access to a network drive. The problem is the network is down every now and then (3 to 6 months). So I've been experimenting with backing up my files on the network drive onto my hard drive using SyncToy. However, SyncToy isn't a great back up option as it does not store multiple revisions/versions of the file by date. Is there a free desktop backup alternative that can make backups and store multiple versions of the files (by date, say)?

SyncBackSE is a great solution for what you are looking to do, but it costs $30.