If you use C# (might work in VB.NET 2008 as well), you can type the name of the fieldIndex, e.g.:
CustomerFieldIndex
(Casing has to be correct), then hit Alt-Shift-F10 and Enter, and the correct "using" statement will be added at the top of your code file. You can tell that you typed it correctly before hitting Alt-Shift-F10 if you see a little red box in the bottom right of your text. You can also click the little red box for additional options, like adding the full qualified class name inline.
This works for all classes, of course, not just FieldIndexes.
I'm sure most people here know this trick, but if you aren't using it already it will save you a lot of time.