I was wondering if it is possible to render a model in wireframe mode during a game?

a simple fixed function effect maybe?

Sorry Quadraxas, I don't know what a fixed function effect is.

I'd say that a FFE is the grandmother of shaders. Quadraxas is right: a FFE which sets FillMode to Wireframe should do the job. I think I've seen something like this being posted at the forum 1-2 years ago, so maybe a search will help you.

Ok. I did search, but I will try again. Thank you both.

If you hit f11 and then (i think i'm not 100% sure) hold alt and shift down and click an entity he turns into wireframe... This is a debug feature.. So go and look for it in the debug.c file or whatever it might be called.

Here is the effect:
just place it in an fx file, load it into a material with it's effect string,
and assign the material to the entity you want in wireframe.
If you have trouble, the manual should help.

technique Wired
{
pass p0
{
FillMode = Wireframe;
}
}