In Resharper 5. see answer below.
-In Resharper 4 use Resharper/Options/Languages/Common/Naming Style
Choose the radio “Override common settings”
this enables the button “Manage Abbreviations”
For a specific language
- Resharper/Options/Languages/C#/C# Naming Style
- Resharper/Options/Languages/VB/VB Naming Style