In my dock... finder have some kind of white bar over him that don´t disappear

It looks like a video artifact mayb related to your video card. There was a recent update for Graphic Firmware released for iMacs running Lion. I don't know if your iMac was one of the machines that required the Firmware update. Have you run Software Update in the last week? Did the Firmware Update appear on the list of updates to download?

How strange. I've never seen that. I hate to say this, but it looks like you have a legitimate claim to visit the Genius Bar and get some free support. Your Mac should be able to pull down updates without that error message popping up.

I'm guessing by looking at the Installer, that it's not for your particular model of iMac. So no harm done, it's not the Firmware update for the graphics that's going to solve this.

If you go to the Apple Menu in the upper left hand corner of the menu bar and choose System Preferences go to the Hardware>Displays. Under Resolutions, choose a size, any size other than the one currently set. Then see if that white bar still appears. Or if there is any change.

Let's try doing something with the Dock itself, Go back to the System Preferences> Personal > Choose Dock

Try sliding the Size: slider and see if the white bar is still there as you change the size of the Dock. Also try out Magnification: slider moving it left and right and moving your mouse across the Dock Icons. Alternately try choosing different positions for the Dock under the Position on screen: settings.

If the white bar is still there, try shutting down the Mac and restarting it. If it's still there it's going to be something related to that Icon itself that OS uses to represent the Finder.

No, I don't. I think I've exhausted all the trouble-shooting steps I can think of related to the graphics card. And if your machine isn't covered by the Firmware update that was released, I don't know what's causing that video glitch. A trip to the Apple Store might be your only choice, see if one of the Genius at the Genius Bar can sort it out.

You can't (and if you could, you shouldn't) change that icon - it's owned by the system.

It's possible that there is a corrupt preference file, which is easy to troubleshoot:

While holding Option, go to the Go Menu in the upper menu bar. Click and open Library (that is your User library, which is now normally hidden). In that folder, navigate to Preferences and move the following files to the desktop:

com.apple.dock.plist

com.apple.dock.plist.lockfile

Restart computer. See if the problem is gone. You can safely throw those two files in the trash and empty (they have already been recreated automatically).

If that doesn't do it, it may have to do with a graphics glitch. I'd suggest contacting Apple - you have a warranty, take advantage of it.

I would say no, you do not need all of them. My personal experience has been that if you don't see the update in Software Update on the Mac either wait until it does show up (sometimes there is a lag, or waiting period before it shows up).

If an software update doesn't show up at all, it probably is not suited well for your Mac. Apple also makes sure to have updates you download directly from the Support website check your Mac before they install. This prevents you from doing harm to your Operating System. It's much safer to be very conservative and just install whatever appears in Software Update.

In the years prior to Software Update one would have to go to the Support website and find the installers and download them, but now it's more automated and reliable. And Good Luck, now I know a little bit more about Candy Bar and how it might interact with the Dock!

Software Update tailors any updates to your particular machine - if it doesn't report that an update is available, then your machine doesn't need it and would cause havoc if you tried to install it.