Hi - You can find general Cite While You Write installation instructions at this FAQ - http://www.endnote.com/support/faqs/CWYW/faq1.asp. Below is an excerpt that I’ve modified for X5 for convenience.
If after following the instructions above the tools still do not appear:
Close Word and EndNote.
Open your hard drive and go to the following folder:
EndNote X5: Applications:EndNote X5:Cite While You Write.
Copy the file “EndNote CWYW Word 2011.bundle” by highlighting the file and going to “Edit > Copy.”
Go to the folder Applications:Microsoft Office 2011:Office:Startup:Word and paste the file, “Edit Paste.” Note: In non-English versions of Word, the folder named “Startup” may be called “Start” or be in the localized language of Word.
Start Word, go to “Word > Preferences” and click on “File Locations.”
If the Startup folder is not set, highlight “Startup” and click on “Modify”. Select the folder Applications:Microsoft Office 2011:Office:Startup:Word and click “Choose.”
I had the same problem, but I was able to fix the problem following these steps. I suggest placing this information in the EndNote X5 pages. I spent a lot of time trying to find it.