Yes, you should have two libraries of "the" type you are thinking of. One is your user library. Generalling speaking you should stay away from the second one--the systems library. Try what the others have said and even other suggestions that come around before what you try the repair install procedure I mention later. Also, your last resort may be to use this link. Personally, I find the link to be very unlearly written for a variety of reasons--most likely because of the variety of points from which individual may be trying to reinstall Lion.
Ignoring the link, my basic idea is for you to reinstall Lion via the upgrade install procedure (i.e., do what at least used to be called a repair install by reinstalling Lion from within Lion). I have not tried a repair install on Lion. So proceed at your on discretion. Whatever you do, be sure that all your data are well backed up, and be sure and think ahead to whatever else you might need if the repair install does not work out (e.g., Safari bookmarks, Address Book archive, iWeb domain file, a copy of the Lion installer, etc., etc.) My educated quess is that if you were to install Lion from within Lion (i.e., the repair install procedure), then you would fix your finder problem without affecting your data, settings, or installed applications, etc.
Since you have installed Lion, you may not have a copy of the Lion installer. But, also since you have installed Lion, you may be able to download an installer using the procedure described below. Be sure and stop Lion before installing if it decides to start an installation before your are ready. Then, you can make a copy of the installer before doing the repair install. Note that the procedure below anticipates that you are going to be using the Lion installer to install Lion on an external drive. But, you would be using the installer to do the the repair install.
"Install OS X Lion
If you completed your installation of OS X Lion, your installer may have been removed after your successful first login to OS X Lion. Mac App Store's Purchases page should show Install Mac OS X Lion as being "Installed", and disallow its download, when viewed from a computer running OS X Lion.
"To redownload the installer on a computer running OS X Lion, press and hold the Option key while you click the Purchases tab. If the button to the right of the Install Mac OS X Lion item doesn't change to "Install" and allow you to download Lion, use Spotlight to search for "Install Mac OS X Lion" on your computer.
- Launch the Install Mac OS X Lion installer you downloaded from Mac App Store. The installer should be in the /Applications folder.
- Follow the on-screen instructions to complete the Lion installation. Be sure you install Lion on the external storage device you've connected for this purpose, not your computer's boot drive.
- When installation to your external device is complete, you can re-run Install Mac OS X Lion installer and upgrade the boot drive of your computer. A Recovery HD will likely not be created, but if you need to reinstall or repair your boot drive at a later date, you can connect the external drive you just prepared and hold cmd-r while restarting computer in order to boot from the external Recovery HD."