My computer was getting slow, not because of ram or cpu, but because of my 5400 rpm hd. So for my 2 year old machine I bought a Crucial CT256MX100 Solid state drive. But I didn't want to lose the storage space in the transition from a 750 gb to a 250gb. And since I rarely use my dvd drive I wanted to use my 750 gb as a dual hd
There were a few bumps and hickups. Like when I striped one of the screws of the speaker/subwoofer. Thankfully I had a series of screwdriver sizes and replacement screws from a teardown of my, now dead, 2007 15" MBP. And The 750 GB HD is thicker than is supposed to fit in the drive bay so it was a long time pushing things together to get cables to reach and my case to seal back together. After putting everything back together It runs like mad. I have it set to use 256 GB of my 750 GB drive as Time Machine backup so I never have to worry about backing up my most important system files.
Make sure to have a good range of screw driver sizes and extra screws. And GO SLOW. When you feel a screw striping, STOP and find a better fitting screw driver.
Also, check the thickness of the hd you want in the drive bay. If it is too thick, it won't seal correctly and you will fun the risk of tearing wires to try and connect things.