From the "oops, we made a BOO-BOO" files:

Apparently some of the PS3 faithful have reported an install issue when trying to play Prototype. What is happening is that the game reports that there is not enough disk space. Unless you truly are down to your last 500 or so MB, then you'll probably slightly vexed to say the least. Here's teh solution: Change the hard drive space by 700 MB.

Simply install another game, demo or remove some online content and try a reinstall. You can also remove media files as well. It is a temporary solution and is straight from Activision, while they work on a forthcoming patch. As it is Activision I expect that the patch will be quickly released.

You can find more info on Activision's website. If you try repeatedly and still cannot install, obviously you should contact Activision directly.