"Why not?" Well, hopefully you have a compatible OS to handle that hard drive...
First thing you'll notice when you get the hard drive is, "Why is it in bubble wrap... and why are the bubbles popped?"
You'll want to run some error scans with HDTune and make sure it's stable :D
Reasons to get Windows 7:
Snap to maximize windows
Formatting huge hard drives
It's Vista but better
The ASUS M4A78-E sucks, don't get it.