But do I really need to get a special high-framerate webcam with a removable IR filter, or can I use the 30fps Microsoft Lifecam I already have lying around?
It depends on what you expect and want..You can try ftn(facetracknoir) with pointtracker plugin with you webcam.If it works like you want it is good.
First I used a ms vx3000 webcam with 30fps, now a ps3-eye with 60fps. I must say that ps3-eye setup works better but with my old webcam it was also good enought.I both had to modify because of a to strong ir-filter.
Also, just how bright do these IR LED's have to be?
What you want/need are three dots good visible, even when you move your head and at the distance you sit from your webcam.You probably need a filter to block the normal light and let the ir-light go through.But that is something you find out when you try your leds with the webcam.
If your leds have a round top, sometimes you need to file them down for a better viewing angle.
For any other question use the search funtion or just ask.