Why are you comparing desktop drives with laptop drives?they use whatever is the cheapest they can get, which usually is the hitachi "deathstar" HDDs, which are known for a really high failure rate. NO, a 12.5mm HDD will not fit. Go with a 7200RPM drive, you will notice the difference from a 5400 to a 7200 drive.
As a note, the entire Hitachi Deskstar line has about a 45% failure rate, where as most other mfgs have about a 15% failure rate.