well mate, you're talking to the right bloke, for best results buy a genuine Vealo clutch from peugeot, the job it's self is fairly difficult, if you are an experienced diy mechanic then it shouldn't be a problem,
http://www.youtube.com/watch?v=znGv4LlTYTY&feature=player_embedded#!
http://www.youtube.com/watch?v=5hQjA6KGQts&feature=channel
there's 2 video guides on how to do it, the job it's self is awkward without the right tools and some knowledge on cars,
if you're just replacing the air filter in the standardair box with a performance one then that's ok because the air box is a good design, induction kit's on this car are a waste of time, take it from me i know, after you have done the clutch and air filter i would suggest a stage 1 tune, it's an easy and cheap mod to do (in fact all it costs is time) and give loads of extra performance,
first you have to find out what pump you have and what turbo then you can make the adjustments accordingly, it's just like remapping a more modern car,
http://www.youtube.com/watch?v=X4l5on3_IrA&feature=related
http://www.youtube.com/watch?v=telXJxsd4gE&feature=channel
adjust the fuel pump first then the turbo, never the other way round, running rich is better than running lean (when at full throttle diesels run lean at any other throttle position)
also disconnect your egr (it's got one) look behind your battery when facing the front of the car, behind there you will find a black solenoid with a green connector, unplug the connector and leave it, that's all you have to do,
what that does it stops the exhaust gas going back into the engine and thus keeping it cleaner
hope this helps
brett
this stage 1 mod i have done to my car if you read my profile it's a worth while mod