how do you use halos in a game?
you don’t:p
Whaddya mean?! there’s no way to use halos in the BGE?
draw a gradient…
what’s a gradient? 
Instead of using halos as you do with the rendering engine, you’ll have to use polygons as your particles, and enable “Halo” in the Texture Face Panel for that polygon. This will make the polygon always face towards the viewer, but you have to have the polygon facing the correct direction (I’m not sure which way is the correct direction)
so how would i for example make a torch in a game without using the particle emitter system?
Animated texture. You can also use sprites being emitted from an empty or whatever.
Edit: You mean fire torch right?
what are sprites? is there a tutorial on this anywhere?
Here is one way to do it:
http://blenderartists.org/forum/showthread.php?t=143770
In next version, or newer svn builds you can have video files instead of picture sequences.