I use the whiteboard in classroom with a screen about 2x2meters. I put the wiimote 3meters away because of the viewing angle and because is a safe zone against students.
In my first attempt with a 1LED pen prototype, the results were dissapointing. I look for a better IR LEDs in the shops of my town, but they have none better than I used.
Then i bought 16 low efficiency LEDs like the first one and build a POINTER. It can be powered with batteries or with an USB port.
The results are impressing: I can click with the pointer touching the screen or at 10cm appart.
I've taken photos of the building process. You can see it in my blog http://antoniubieto.blogspot.com. There is also an electronic schematic and calculations. The drawback is that the explanations are in catalan (very simililar to spanish).
I hope that it'll be useful.

Antoni.