Hi
Remove your gear stick surround and pull out your centre dash, radio maybe out an heater dials off. The bulb is on the top of the dial, it depends how old it is but can be either a twist and pull bulb holder or just a striaght pull out holder
It doesn't take to long though
Good luck
isn't that for the heater bulbs mate?
for the oil temp gauge then it's a sealed unit with 2 surface mount L.E.Ds inside... you need to:
Remove the gear knob
Remove gearstick gaiter
Remove your CD player (not necessary but recommended)
Remove the Center console and unclip the switches etc
unscrew the 4 screws at the top of the console and that gets you the oil temp gauge out the car
now you need to open the gauge up (its about a 6 step process) then de-solder the original surface mount LEDs and solder on new ones you can get them from maplin for pennies
this site should help you out massively... it's he guide i used to replace mine with red ones
http://www.mgf-tf-central.co.uk/iainross/gauges.html
It's a tricky job as far as soldering is concerned but if you find someone who knows what there doing you should be ok (hint: tweezers and a steady hand are your friend lol)
anyway, hope that helps