Currently Being ModeratedSep 11, 2012 9:31 AM (in response to tique)
Yes but it's definitely not advised. If you have a machine newer than 2009 Apple uses drives that have integrated heat sensors. This makes upgrading much more difficult but not impossible. If you have a machine still under warranty then definitely DO NOT do this yourself as you may void the warranty not to mention it isn't for the faint of heart. Take the machine to an AASP to have the work done, you will need to find one in your area willing to do so.
If you are considering a new machine then simply buy the configuation you need.