Do you mean that you accidentally deleted the actual program from the Applications folder and then emptied the trash? I'm asking just in case it might be rattling around someplace on your hard drive. Do a Find for it. If not, iWeb is part of iLife, just re-install it from the CD, then do the update to bring it up to speed! http://www.apple.com/support/downloads/iweb111.html
Also if you've done any work on iWeb, it might be a good idea to try and retrieve the "domain" file. Spotlight it, your lucky if you find it! Then just put it back into iWeb > Application support once your re-install iLife
Also if you've done any work on iWeb, it might be a good idea to try and retrieve the "domain" file. Spotlight it, your lucky if you find it! Then just put it back into iWeb > Application support once your re-install iLife