ffs I just wrote a massive reply to this, pressed submit then closed the tab. Unfortunately welly's reply meant it needed re-submitting. arse.
In short:
You can get a cambelt kit from the dealer, about £25. You'll want to buy a pile of wheelarch liner screws as well, as they rust quite badly. You also want to throw a new water pump in while you're there.
I don't think the aux belt tensioner is replaceable, but a bit of a clean-up, some WD40, and a lot of tugging will un-seize it and you'll be able to feel how strong it is. Mine's VERY strong. To replace the aux belt you'll find it easier if you rip the ECU and its box out.
The upper cambelt cover is a bitch to take off because of the bolt in the middle of it. Save yourself time by putting a jack under the sump to take the weight then remove the upper engine mount. 3 bolts at the back, a nut on the dome, and 4 screws on the engine. Loosen the joints before though as it'll make it a lot easier and stress them less.
Be wary that this may all be in vain unless you have access to hefty tools. I'm a BIG bloke and I couldn't shift the camshaft pullet belt with a 3 foot breakers bar.
My tubby had its last belt change well over 100,000 miles ago. Never hurts to check its condition though!
Actually I can sell you a timing belt kit and water pump! My tubby's dead now so I won't be needing them

<steve_earwig> I think this forum is more about keeping our cars going with minimal outlay than giving our cars more reason to go bang