This is an interesting project if you have some spare time to play with this – Lucene is a facinating open source project from the Apache stable that builds and searches full text indexes.
OnJava.com have an article showing how you can use the Lucene engine and API to build a facility to index and search source code. It would be interesting to compare how this is similar/different from the source search facility in Eclipse, as I believe the search facilities in Eclipse are also based on Lucene.