Q: iPhoto is gone

No. Reinstall it from the computer's original disks or an iLife install disk.

(88056)

What system came preinstalled on your Mac?  If it was Lion go to the App Store and download from Purchases.  No need to repurchase.

If it was SL or earlier follow Niel's advice.

If it was the disks that came with your Mac there will be a disk that contains the iApps that you can use to reinstall iPhoto.  It will look like one of these:

There won't be one. As stated above, reinstall it from the computer's original disks or an iLife install disk.

(88058)

You can either purchase the iApps separately from the App Store or purchase an iLife 11 disc from a 3rd party retailer like Amazon.com: iLife 11.  The latter option will give you iDVD and iWeb which are no longer offered by Apple.