Hello Paul,
You can install EndNote X8 (as in 18) and Reference Manager 12.0.3 on a 32-bit version of Word 2010 simultaneously. Make sure you have Reference Manager updated and Word is the 32-bit version:
http://help.thomson.com/default.asp?portalid=TSC&article=105162
It is possible Word has disabled the EndNote tools. If so, you can try enabling them:
Otherwise, there may be a conflicting third party application loading as an add-in in Word 2010. Be sure Office/Word are updated to the latest version available.