Somethings wrong with my desktop. Can someone please help?

Question

Ok first of all let me start by saying I'm the most tech illiterate person on the face of the earth. This may have been already posted somewhere, but my complete lack of experience dealing with Mac os operating system may have caused me to completely coast right over it. So please have mercy on this poor lost mac dummy!
Yesterday a software update popped up with several updates listed so I gave them the go ahead to install the latest versions of Itunes, safari, mac os (10.5.8) The update appeared to go smoothly so since it was late I called it a night and let it sleep. To my surprise when I woke it up today I realized that none of my DESKTOP ICONS appeared to be working or responding when I clicked them, and in fact after trying to open itunes and some other frequently used programs the icons changed from their usual selves to a blank *notepad with a ruler and two pencils* (see this is how dumb I am, I don't even know what that silly icon represents) I guess thats the default when items go missing?
After much panicking I somehow managed to open the finder where I checked my 'applications' and 'documents' and was relieved to see that they are all still accessible and operating correctly through the finder, and nothing was gone. Its just that they are no longer usable through their desktop icons. I mean I checked the "desktop" area of the finder and its completely blank.
I'm so lost as to where I go from here and was wondering if someone who knows how the system operates could give me a "dummy" version of how to put them back onto my desktop like they were before the update? and where I went wrong to cause them to go missing in the first place?
Years of 'Windows' operating crashes and painful unintended erases (where i've lost all my data) have made me extremely fearful (and hesitant) of messing with system configurations in general, and although Mac is completely more stable I'm still scared about doing something wrong and erasing everything.
If someone could help me as to what to do next I would be eternally greatful!

Answer 1

We need clarification. When you say Desktop icons do you mean the ones on the Dock? If so, then do the following. Restart and see if that fixes the Dock icons to their original and not the generic application icon (it's a pencil, paint brush, and ruller on two blank pieces of paper) stored in /System/Library/CoreServices/CoreTypes.bundle/Contents/Resources/ named the GenericApplicationIcon.icns file. If they don't change, launch Disk Utility, select the boot volume/partition, and repair permissions, restart, and see if that fixes things. If not, then launch the Terminal.app in /Applications/Utilities/ (which is what you see when double-clicking on the root-level disk icon sitting on your Desktop and not the Finder). Select and copy this one-line command, paste it into the Terminal window, hit the return key, quit the Terminal app, OPTION-click and hold the Dock's Finder icon, and select Relaunch:
*/System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/LaunchS ervices.framework/Versions/A/Support/lsregister -kill -r -domain local -domain system -domain user*
This will rebuild the LaunchServices database and should restore all the Dock's icons to properly display the apps that they represent.