If you want to learn about the SPARQL (SPARQL Protocol and RDF Query Language) now is a great time to do it as there are some new materials available:

• Introduction to RDF Query with SPARQL Tutorial as given at WWW2005 by Steve, Eric, Andy and myself on Monday. All available for reuse.
• SPARQL RDF Query Language Reference, a 2-page summary document that I made of SPARQL including the concepts and syntax as well as Turtle RDF syntax.
• Search RDF data with SPARQL article by Philip McCarthy for IBM developerWorks using the ARQ Java query system, using Jena.

You can run these using multiple online demos (linked) or with several open source SPARQL implementations. Most of these are linked from the SparqlImplementations wiki page or from the Gargonza Experiment project which is a showcase for RDF and SPARQL.