There is no limit on the times you can install it from the DVDs. There's just a limit as to being able to run it on multiple machines AT THE SAME TIME. If your old computer dies, or you sell it (please reformat the drive so they don't get FCP for free), then you can install on a new computer fine. And you are allowed to install on (1) desktop and (1) laptop at the same time as well...but only use it on one machine at any given time. Meaning you can use it on the desktop at work, and then when away from the office, on your laptop.
Long story short...you can install it fine without any issues.