Looking in your computer case to verify the hard drive is atleast 2.5 inches won’t be too hard. The only thing stopping you is your will. What is not stopped, however, is time and as it goes we will come to find flash cards & SSD emanating into the economy. With the volatitly and reliability, the best option (not right now, but for the future) is the flash card or the Solid State Disk. The various companies, (Scandisk, Canon, etc) have no problems producing these disks as they are the smallest in size and fastest in speed.
At the moment, it doesnt seem that Solid State Disks, and (some) flash card are worth it; lets just say that some of them could cost you the same amount as getting 2 Veliciraptors. But, come the future, and we will see flash cards and solid state disks being the primary memory chips. You see these chips mostly in the mobile industry, but as a revolutionists, (not me, but…) someone is going to make an entire 300GB hard drive based on a flash card.
Its only a matter of time, but hey, what are you waiting for?