The average diesel car leaves the factory using only approx 50% of it's potential, so most diesel cars can get 25% more bhp and 18 to 20% extra torch.
Remap - change of software in the ECU
Chip - usually a plug and play chip that fits between injectors and ECU.
As your motor is 2005 you would have a remap of the software of your ECU. First of all the software already on the ECU is uploaded and either downloaded with a off the peg remap or sent over the Web to a tuning and software expert who does what you have requested. Either way the new software is going to change the performance of your motor for the better, and also increase your fuel economy when driven normal.
You can request a fuel economy remap or a performance remap.
It will reduce the engine life, however diesels are so long lived that losing 20.000 off the life of the engine is acceptable.
Your motor is never going to have the kind of performance that is going to worry a scooby, however it will be a much better drive and nippy when you need it.
Check this site, they did mine and very pleased.
http://www.chiptuners.co.uk/