Windows 7 Professional has a built in backup utility that works well. I use shadow copy on the primary hard disk and run my backup jobs to a secondary drive. That way I have versioning and full backups. Its a bit redundant but I was bored and wanted to try it out. You can even do a system image with it.A better alternative is to run your old disk as a slave (not bootable). This will just show up as drive D or G or something. Reformat it and then use a downloaded backup utility to run incremental backups ever night or specified time interval. Only back up your c:\Users\? directory (where all the data is stored). Should your disk fail you can reinstall windows easily on the new disk along with your programs from their original DVDs or the Internet and simply then restore the data from your backup.
The other downside with mirroring is that a HD failure is not the only thing to be concerned with. Data corruption and virus' are also things to be concerned with, and if you get hit with that, the mirrored drive will also get hit.You can set these drives up for disk mirroring in bios. Basically the computer will keep them synced for you automatically as your files get updated. The two downsides to this is disk access speeds drops slightly on disk writes, but not reads and if you do a simple chkdisk to fix faulty sectors you must first disable mirroring or risk corrupting the mirrored disk.