FRIDAY!
Just about everything that's been said about Macs in this thread is wrong!
I tried restarting, and it's not getting past the "Starting Mac OSX" screen.
I was on a different wireless network all weekend. Could that have something to do with it?
If you aren't getting past "Starting Mac OSX" try booting holding down the Shift key, that will turn extensions off.
The wireless network thing will have nothing to do with it whatsoever.
Delete the present versions of those programs then download new ones. Reinstall both of them. Or, if it's something deeper... I don't know. Macs are notorious for crashing all the time.
iTunes you could reinstall, but DVD Player is part of the system. The way to test if it's the application's fault is to create a test user by going to System Preferences > Accounts. Log into the test user and start iTunes and/or DVD Player. If they run, the apps are fine, it's a setting within your user that's failing.
Macs, when maintained well and kept tidy, are very, very, stable.
Sounds like you'll have to use the original install CD to repair the install, if Macs are like any other operating system.
I know what your getting at, but the Mac equivilent to the Windows XP "Repair Install" is the Archive Install, where the install disk plops a fresh system folder in the root and renames your old system folder, "Previous System Folder".
So not Repair, but Archive.
If you reinstall your OS, yes, you could lose your files.
That is wrong, fortunately for you. An Archive Install will not touch any file you have on your hard drive. The only thing it does apart from adding a completely new system folder is renaming your old system folder. An Archive Install is completely safe.
We can get you working again Friday, we can do it.
Try booting holding down shift. After that, try booting to your OS X install DVD. Once booted to the Installer, run Disk Utility and Repair Disk.
After that, the hammer. Just kidding.