1. Download Linkit
Download Pathologic from this page http://drupal.org/project/pathologic
Download the module from http://drupal.org/project/linkit
Install and enable linkit and at least one of linkit_node, linkit_views, linkit_taxonomy or linkit_user
2. Install using the "Install Module" facility
Go to "Modules" and then "Install new module."
2. Browse and upload
Browse your local computer and choose one of the files you just downloaded.
First upload Pathologic.
Then upload Linkit
If you upload Linkit first you will get an error message saying that it did not upload. If you upload Pathologic first you will not get an error message.
3. Enable Pathologic and Linkit
Enable Pathologic first, by putting a check in the checkbox, then scroll down the page and click the check marks on all the Linkit check boxes.
Scroll all the way to the bottom of the page and click on "Save Configuration" Notice that after you've saved, all the words "disabled", in red, are replaced with "enabled" in green.
Now you need to put the access icon on the editor's menu bar.
4. Add the link icon to your WYSIWYG editor
On the same "Module" page, scroll until you find the "User Interface" section and click on the Wysiwyg "Configure" link.
Choose the WYSIWYG profile you want to use Linkit on and click on "Edit". You can use it an any or all of them. After you enable it on one profile, repeat the procedure on any other profiles you want to use it on.
Expand Buttons and Plugins by clicking on it. Then scroll down and find the Linkit checkbox. Enable it by clicking the checkbox.
Check the box and scroll down to click the "Save" button.
You will know you are successful if you see an additional link icon on your toolbar. You will now have three icons that deal with links, the default link icon, the unlink icon and the Linkit icon. If you want to remove the default link you can uncheck it from Buttons and Plugins page, but you don't need to do that. It will still be functional.
When you click linkit you will see the "Browse server" button on the dialog box.