As has already been noted, anything rubber will have perished and will need replacing, as will all the fluids and any other normal perishable items (brakes, battery, filters etc). The brakes will have siezed on, and depending how dry the garage was, the interior may have mould and the bodyshell may have gone rusty...
The biggest risk, however, is that the engine may have siezed, depending on how it was treated before it was parked up.
My approach would be as follows (in no particular order):
Brakes
Un-sieze the rear brakes. a 3lb club hammer is useful here. Assuming it has drums on the back, free off the handbrake linkages and grease them. Replace the cylinders and pads and check the condition of the drums.
Remove the front calipers, check the condition of the disks and replace if necessary. Either replace or re-seal the calipers depending on the condition of the bores. Fit new pads.
Replace or re-seal the master cylinder (again depending on the bore condition). Check the servo (this is easiest done with the engine working).
Replace all the rubber hoses and carefully check all the solid lines. I'd use braided hoses on a car like that rather than standard rubber ones. Bleed the system completely with new fluid.
Tyres
- Replace all 5. Don't be tempted to keep any that look OK, after that long they will be perished.
Transmission
Check the condition of the CV joints. They ought to be OK, but you'll probably need to re-grease them and change the gaiters. Same for things like steering joints and track rods.
Empty the gearbox oil, flush and re-fill with the correct grade. The box should be OK, assuming it was fine when it was parked up.
The clutch is generally hard to check without removing the box. Once the engine is running, you should be able to tell if it is working... If it is hydraulic, you'll probably need to replace the seals as per the brakes. A cable clutch should be OK, but a few drops of oil run down the cable will help - disconnect the clutch end and hold it up, run oil down it then pump the pedal a few times to work the oil down the cable.
Engine
Drain the oil and coolant, flush both through and re-fill with water and thin, cheap oil (which you'll replace as soon as it is working!). Remove the plugs and dribble a little oil or diesel into each cylinder, then wait a few days - hopefully the oil will vanish down the bores. Using a socket & bar on the crankshaft end bolt, carefully try to turn the engine. Once it turns freely by hand, connect up the new battery and try it on the starter. Once that turns freely, put new plugs in and try starting it (after sorting the fuel of course...).
Run it up to temperature watching carefully for any fluid leaks. Check for signs of head gasket failure, water pump failure etc.
Allow it to cool and check the oil and water condition. Both will be filthy ;) If there are any signs of contamination in either, check why. Once you're happy, drain and flush both again (but refilling with proper coolant this time), then again after about 500 miles.
Fuel
- Any fuel left in it will be useless. Drain the system, replace the filters and any rubber hoses and refill. The injectors will need cleaning, and check none of the pipes have become gummed up.
Turbo
- The seals in the turbocharger will be perished. I'm no expert on turbos, but I presume it'll need dismantling and refurbishment.
Bodywork/Interior
- This entirely depends how well it has been stored. If you're lucky, all it'll need is a good clean. Otherwise it may need a lot of welding and/or replacement interior.
Overall
The most imporant question you need to ask - Why was it parked up in the first place? Chances are, something broke...
I have a car I'm in the middle of re-commissioning that has been parked up since 1992, so I've been through most of those already. Luckily my engine wasn't siezed and the interior is OK, but it needs a fair bit of welding...
