Basically whats the difference between the Western Digital Caviar Blue and Western Digital Scorpio Blue?
On this website where i will be shopping, it shows WDScorpio Blue as being more expensive, while WDCaviar blue shows to be completely out of Scorpio's league state wise, caviar blue has 7200RPM while Scorpio has 5400RPM, caviar has 16MB cache while Scorpio has 8MB, caviar has 6GB SATA interface, while scorpio doesn't even state what kind of SATA interface it has.
Caviar blue will be much faster due to the 7200RPM + double the cache rate vs the Scorpio's 5200RPM.
Personally I wouldn't get anything lower than a 7200RPM HDD these days, their slowness isn't worth the time in the long run.
The SATA interface wouldn't really matter as well - the very basic SATA I connection tops out at 150MB/sec which most HDD's don't reach (maybe in burst).
Edit: I missed that louis_96! Good catch.
The Caviar Blue is meant for desktops (or even very large laptops/desktop replacements), while the Scorpio blue would fit in most laptops. The Scorpio blue can also fit in desktops - with a 2.5" bracket.
You have to watch out though - some laptops can only fit a 7mm height 2.5" HDD, or the 9.5mm height 2.5" HDD. Some are interchangeable though.
Caviar series drives are in the 3.5" desktop form factor, while the Scorpio series drives are in the 2.5" laptop form factor.
SATA II vs. III for hard drives is basically irrelevant because no hard drive has transfer rates that get anywhere near the bandwidth of SATA II, let alone SATA III. It's only for ultrafast devices such as the fastest SSDs where SATA II actually becomes a bottleneck and you need SATA III to get full performance.
You can download a paper from this Microsoft web page that tells you how to configure your SATA ports as removable or non-removable by configuring the Registry.