[news.eclipse.helpwanted] [classname] cannot be resolved - where classna

[Alex Hunsley <lard@xxxxxxxxxxxxxxxxxxxxx>]

I'm trying to set up a new java project in my workspace for eclipse.
(I've been using it for ages now and love it.)

As usual, I created a new java project in the current workspace, then I 
add a folder to it, selecting "link to folder in file system" where some 
.java source files are. This folder then appears under my project 
correctly (with all the source files in the file system appearing under 
that folder in the project view). However, when eclipse tries to compile 
this project, I get a million and one errors, all saying either:

 The import x.y.z cannot be resolved

or:

 [classname] clannot be resolved

All the imports and classes it cannot resolve are part of the project! 
They source files are there, in the right place with the correct package 
declarations in them, so I am fairly stumped. I've looked hard at the 
project properties and nothing seems amiss.

Any ideas?

thanks
alex