My hard drive failed and so I needed to replace it. I soon found out that the hard drive cable was also bad (seems like a common issue for the 2009 MBPs).
The guides at iFixIt to switch out the drive and cable were great. The 54 bit driver set worked out very well and I do wish I had purchased something like this a long time ago.
If you are going to switch out your drive, definitely consider a SSD - I found macsales.com to be a good place for this.
The hard drive cable isn't sold by Apple directly which is unfortunate. The cost of the cable is ridiculously high so shop around. I purchased mine on Ebay and it appeared to be brand new - many places sell refurbished or used cables so be sure to look for that.