Perhaps you've already had this question answered by now.
However, in case any one else is looking for an answer (as I was):
The problem may be that you need to add a reference to the ArcObjects library to the project.
In Eclipse, you can add the reference by right clicking on your project in the Package Explorer.
Scroll down to 'build path'
In the pop-up menu, select 'Add libraries'
In the Add Library dialog, select 'ArcObjects Library', then click 'Next', then 'Finish'.
This worked for me anyway.
I am using Eclipse:Kepler Service Release 1 with ArcGIS 10