The mirror is held on by 3 cross head screws, which are behind the black plastic triangle inside the car. This is held on by 2 clips top and bottom. To get it off, pull away the rubber trim and insert a flat bladed screwdriver and just simply pull/lever it off. Be careful though as there is painted metal behind the trim and if you are too enthusiastic with the driver, you will scratch the paint.
Once this is off it's fairly straight forward except that on my car, the screws had 'rusted' in. There had been some sort of chemical reaction with the white metal casting. I got two out easily, but the third was an absolute bugger and I ended up rounding it off. In the end it came out, but I would recommend that you use a really good screwdriver to make sure you get a good contact. When I put it back, I put copper lube on the screw threads, and replaced the damaged screw with a allen headed fixing.
Putting the black plastic trim back is easy, just make sure you put the bottom edge in first, as it has a felt seal which inserts into the door trim.
I seem to remember that someone else posted to the forum saying that they had successfully glued the white metal mounting using something like araldite.
Hope your Birthday was ok by the way !