I back up most of my data on another hard drive that's in another computer. I could also use an external drive.
The important irreplaceable data is also put on DVDs.
Normally I don't back up more than once a month because I don't generate enough important data to justify it.
I keep my drives fairly cool. I monitor their temperatures occasionally. Most run below 100 F. One of them gets up to 104 F sometimes. That should be good enough.
I run a hard drive diagnostic every couple of weeks. I check the SMART status, and I run the drive's built-in self test. I've never had a drive die unexpectedly. The diagnostic tests have always warned me and given me plenty of time to save my data.
Western Digital has a diagnostic that runs under XP. I recommend it. Assuming it can access the SMART, it will run the drive's built-in self test when you run the "quick" test. That's all I do. Make sure the SMART status is good, and run the quick test.
Most external enclosures won't allow access to SMART, and some PCI to IDE controllers won't either. I avoid both.
Here's WD's diagnostic.
Seagate also has a good diagnostic that runs under XP, but they are in the process of upgrading it, and it isn't available currently.
These diagnostics are useful with any drive, not just the ones made by them.