Don't give up. What you're seeing is not normal, and we can probably fix it.
First, when you hold Control while clicking the mouse (or right-click) over a file/folder name in a Finder window, you should get a small "contextual" menu with several options you don't see elsewhere. If that's not working, it may be related to your other problem -- that's why I asked if the scrollbar moved automatically in this case, too.
Second, try using the column view in a Finder window. Move around in it, click file names, etc., and see if it moves around. Then go back to list view and see if the problem persists.
Third, if you have a two-button mouse, temporarily change the primary button via System Preferences>Keyboard and Mouse>Mouse. See if the problem persists with the other button.
Fourth, the Universal Access Mouse panel has a very helpful feature: if you select the Mouse Keys On button, you can use the numeric keypad instead of the mouse. The 5-key is a mouse click; the others move the mouse. Also, if you check the "Press the Option Key 5 times . . . " box, you can turn this feature on or off if your mouse breaks, so you can still control your computer.
Turn this feature on, then use it to perform the same actions on a Finder window that cause trouble when using your mouse. See if you get different results.
Last, if you don't want to create a new user to see if the trouble is with your Preference file, move the following file to your desktop:
<your home folder>/library/preferences/com.apple.finder.plist
Then relaunch the Finder (via the Force Quit menu). It will automatically make a new plist file.
If the problem stops, trash the file you moved to your desktop (it's corrupted) and re-enter your Finder preferences. If it persists, trash the new one and move the old one back.
